Wednesday will be informed that not only several but everyone in the entire world is in a position to have special knowledge on the subject via direct prayer-derived experience. She will also be informed to seek out these experiences for herself as ones persons experiences can not be applied to another person. Further those experiences should not be a general feeling of good-will, feeling at one with the universe, strong emotions, uncontrollable crying, etc. as those are not the characteristics of the spirit per LDS doctrine (or dogma if you insist). Instead the experience, whether it includes visions or just the still small voice of the spirit should provide her with knowledge that she could not other wise obtain that is actionable and if testable turn out to be correct as well as making sense. Not everything is testable as we are not able to go back and make a different decision to see what would have happened. As a desire to believe is sufficient to be baptized she will most likely be baptized even if she has not actually had such experiences, but if she takes her religion seriously (which hopefully she should) then she will seek such experiences and from my own experience she will receive them if she does so in the correct manner (being actually wanting an answer and willing to follow whatever the answer is, assuming the answer fits the criteria of what is an actual answer and what is not.
Further if Wednesday's parents are familiar with the doctrine enough then they should welcome you or anyone else that has a different view of the world in to present that view to them and Wednesday. The Church of Jesus Christ of Latter-Day Saints claims to deal in truth wherever it is to be found so if you have some truth they should welcome it and if you have falsehoods then they should be easy enough to correct. Further, if her and her parents take the doctrine seriously they should not make fun of you for doing so, though they may present their beliefs and reasoning’s for them to you. As per one of the central tenets: “We claim the privilege of worshiping Almighty God according to the dictates of our own conscience, and allow all men the same privilege, let them worship how, where, or what they may. “ -Articles of Faith, 11
Further if her parents understand their religion they should not shun or ostracize her should she decide not continue to be a saint. Please be aware that not everyone understands this with in the LDS church, we do not claim to be perfect people but to be people seeking perfection.
It sounds like you're saying you've received testable knowledge you couldn't otherwise have received in this manner. Would you mind expanding on that?
(Disclaimer: This post is sympathetic to a certain subset of theists. I am not myself a theist, nor have I ever been one. I do not intend to justify all varieties of theism, nor do I intend to justify much in the way of common theistic behavior.)
I'm not adopted. You all believe me, right? How do you think I came by this information, that you're confident in my statement? The obvious and correct answer is that my parents told me so1. Why do I believe them? Well, they would be in a position to know the answer, and they have been generally honest and sincere in their statements to me. A false belief on the subject could be hazardous to me, if I report inaccurate family history to physicians, and I believe that my parents have my safety in mind. I know of the existence of adopted people; the possibility isn't completely absent from my mind - but I believe quite confidently that I am not among those people, because my parents say otherwise.
Now let's consider another example. I have a friend who plans to name her first daughter Wednesday. Wednesday will also not be adopted, but that isn't the part of the example that is important: Wednesday will grow up in Provo, Utah, in a Mormon family in a Mormon community with Mormon friends, classmates, and neighbors, attending an LDS church every week and reading scripture and participating in church activities. It is overwhelmingly likely that she will believe the doctrines of the LDS church, because not only her parents, but virtually everyone she knows will reinforce these beliefs in her. Given the particular nuances of Mormonism as opposed to other forms of Christianity, Wednesday will also be regularly informed that several of these people are in a position to have special knowledge on the subject via direct prayer-derived evidence2 - in much the same way that her parents will have special knowledge of her non-adopted status via direct experience when she wasn't in a state suitable to notice or remember the events. Also, a false belief on the subject could have all kinds of bad consequences - if the Muslims are right, for instance, no doubt Hell awaits Wednesday and her family - so if she also correctly assumes that her parents have her best interests at heart, she'll assume they would do their best to give her accurate information.
Atheism tends to be treated as an open-and-shut case here and in other intellectually sophisticated venues, but is that fair? What about Wednesday? What would have to happen to her to get her to give up those beliefs? Well, for starters, she'd have to dramatically change her opinion of her family. Her parents care enough about honesty that they are already planning not to deceive her about Santa Claus - should she believe that they're liars? They're both college-educated, clever people, who read a lot and think carefully about (some) things - should she believe that they're fools? They've traveled around the world and have friends like me who are, vocally, non-Mormons and even non-Christians - should she believe that her parents have not been exposed to other ideas?
Would giving up her religion help Wednesday win? I don't think her family would outright reject her for it, but it would definitely strain those valued relationships, and some of the aforementioned friends, classmates, and neighbors would certainly react badly. It doesn't seem that it would make her any richer, happier, more successful - especially if she carries on living in Utah3. (I reject out of hand the idea that she should deconvert in the closet and systematically lie to everyone she knows.) It would make her right. And that would be all it would do - if she were lucky.
Is it really essential that, as a community, we exclude or dismiss or reflexively criticize theists who are good at partitioning, who like and are good at rational reasoning in every other sphere - and who just have higher priorities than being right? I have priorities that I'd probably put ahead of being right, too; I'm just not in a position where I really have to choose between "keeping my friends and being right", "feeling at home and being right", "eating this week and being right". That's my luck, not my cleverness, at work.
When Wednesday has been born and has learned to read, it would be nice if there were a place for her here.
1I have other evidence - I have inherited some physical characteristics from my parents and have seen my birth certificate - but the point is that this is something I would take their word for even if I didn't take after them very strongly and had never seen the documentation.
2Mormons believe in direct revelation, and they also believe that priesthood authorities are entitled to receive revelations for those over whom they have said authority (e.g. fathers for their children, husbands for their wives, etc.).
3I have lived in Salt Lake City, and during this time was, as always, openly an atheist. Everyone was tolerant of me, but I do not think it improved my situation in any way.