Slower processing evidenced by slower response or stated confusion would be the most likely result. Polysemy is actually good for helping kids practice using context cues, so it is arguable that even if she was making errors, it would still be a good thing from an educational standpoint.

It is worth noting that when linguists complain about how bad English is, they do not complain about polysemy, but about deep orthography and some nasty grammatical rules. It is also worth noting that English is pretty much average as far as polysemy goes, at least in European languages -- although this may depend on whether you consider idiomatic phrasal verbs to be polysemies of the composite words.