Trying I really admire your volunteering like this, it shows thorough dedication. I can understand exactly how you feel after all the hard work you put into it. I can see as well that you are a good person and tolerant. Dont let this woman as Bebop says make waves. Talk to the Pastor I am sure he would want to solve this situation straight away. It is not everyday a good volunteer walks in the door where ever, church, synagogue, mosque.

Dont lose sleep over this and dont end up wasting your time resenting this other person, you are too good a person to have to deal with that emotion.

Speak to the Pastor.