Tangentially, the fact that she is arguing with a person that believes in evolution could itself be a problem that changes the dynamic.
I've often observed that most people believe in evolution in essentially the same way a creationist believes in creationism. They did not reason themselves into that position nor do they really understand evolution in any significant way, it was a position they were told all right-thinking people should believe and so that is why they do so. The charge often forwarded by creationists that evolution is merely another quasi-religious belief comports with reality in many cases, unfortunately. Nominal evolutionists that are clueless about evolution and just parrot talking points can often destroy the credibility of scientific evolutionists that come later.
Understanding the qualifications of the person she is having a discussion with is helpful from a tactical standpoint -- it determines the nature of the defense of creationist ideas.
Being a veteran of many creationist arguments, I would make the point that there is no need or reason to bring religion into it nor even to talk about "losing an argument". You can ignore it entirely if you choose to and it usually keeps the defensiveness down. Also, stay away from any arguments that have well-known creationist defenses; it will force her to think about what you are saying rather than giving the opportunity to borrow what someone else has said. Keep the tone matter of fact so that it doesn't sound like you have an emotional investment in it -- very important. If you really want to play it clean, don't even frame it in terms of what you think or believe; just discussing chains of reasonings over reasonable facts without inserting a value judgement helps make the other party think they are reasoning to the conclusion themselves rather than you imposing your beliefs.
Most of the work is framing. If you make it completely orthogonal to what anyone believes, religious or otherwise, and turn it into an emotionally-neutral logic puzzle, you can often bypass the memetic defenses long enough to make a difference. It does not matter what you believe if we have this interesting set of scientific facts...
I have a creationist friend with no particular rationalist or scientific training. She recently asked me to send her a "list of evidence for evolution that persuaded me." After some prodding, it was revealed that she's getting into an argument with another friend of hers who believes in evolution. I'm assuming that she wants the experience of arguing with someone who's on level footing with her. It seems like a good opportunity to broaden someone's mind in a more general way that'll benefit them in the long term. I don't particularly care whether she believes in evolution (it probably will not impact her or the world in general if she changes her mind about it). But I'd like to phrase my e-mail in a way that's most likely to cause her to re-evaluate her worldview.
Subgoals related to this:
1. Point out that "losing" an argument can allow you to learn things, and if you honestly care about truth you'll try your best to evaluate ideas from other points of view and consider what it would mean if they were true. Do this without sounding condescending.
2. Give her a line of retreat by proposing that evolution is compatible with the Original Sin interpretation of genesis (which is very important to her and I would never attempt to argue against).
3. Give as much background as possible on the scientific method.
4. Still manage to focus the bulk of the e-mail on the most persuasive facts supporting evolution, otherwise I'm obviously not satisfying the criteria she actually gave me. I don't mind taking advantage of her request for my own purposes, but only if I'm actually helping her with her stated goal.
5. Specifically show why macroevolution is not only possibly but likely. (I'm pretty sure she either already believes or could be easily persuaded to believe in microevolution)
6. DON'T focus too much on why creationist arguments are flawed (she hasn't even used any yet, and it sends the wrong message about trying to actually figure out what the truth is)
7. Accomplish everything in approximately 3000 words, without using jargon, designed to be read by someone who's mental architecture isn't particularly adapted to rationalist thinking. (Most people aren't.)
I believe I can do a decent job myself. But it'll be a fair amount of work, and I want to know if anyone had a recommendation for a particularly good essay that I can either link her to or borrow pieces from. I might also include a link to a page of common bad creationist arguments and why they don't make sense.