Eek.. well, I am sorry that you felt so used and under-appreciated honey! That is awful. Thanks for sharing your feelings though, it will hopefully help all of us brides keep things in perspective.
I will say one thing though, I think that communication is so important in EVERY relationship that anyone has (husband, wife, fiance, friend, co-worker, brother, sister, etc...). If anyone (whether I was in their wedding or not; MOH or not) asked me to do something I did not feel comfortable with; could not afford or did not feel like I should do - I would very honestly tell them how I feel and if they were a good friend they would understand and we would find a way to compromise that we both feel good about.
If her friendship means a lot to you (I am assuming it does given you were her MOH and she is yours); please do not email her. Email can be very deceiving and things are almost always taken the wrong way. Sit down and tell her how YOU feel without putting her down. Just explain that you felt "xxx" when "xxx" happened.
I hope you can work it out and again I am so sorry that you were made to feel so badly!