It was unlikely that what you said would have gone over well, but I feel that you did the right thing by telling her about your experience. Going any further than that would have been overstepping, but you didn't do that. You gave her fair warning and dropped it to let her continue on as she wished to.
Hopefully this won't impact your volunteer work too terribly much. If her not speaking to you starts to become an impediment, I think it would be okay to ask for a different shift/pairing.