Even as I read your email, I was thinking "uh-oh, this isn't going to end well."
I suspect that your well-intentioned message, even if it didn't mention her name, was not received in the spirit you would have hoped. Also, as teacher rep, I imagine it wouldn't be much of a leap for others to think you got the info from her.
As the others said, you'll have to talk to her to find out. But I have a strong feeling that she believes you stabbed her in the back. Sometimes it's only subtle interpretations that set these things off - but I'd bet this is one of them.
You won't know what she is mad about unless you ask her. There is no excuse for her to disregard your child regardless of what she is annoyed over. But, I believe in being the bigger better person, so I would just ask her why she is mad at you? You can just say I am sorry you are mad about XXX, however you brought it to my attention and I needed to resolve it with the staff and find out then how we can alter what we do to serve you better. If she still wants to stay mad then I would look at it as her problem. You tried, you made an effort to fix it.
We had a minor problem with some staff at the beginning of our school year. I had a teacher come to me who told me this... She said when her children were younger before she became a teacher she was very involved in the PTO and served as president at some point. so she knew first hand how much work and dedication we give that can go unappreciated by some teachers. She said the handfull of teachers who have volunteered in their life know exactly what you do. However, the mass of them that have never volunteered a day in their life have no idea what you do and therefor do not appreciate what you do the same way.
If you have found that they do not care about this program, then survey them as to what ideas they have for something better you can do. You can even discuss it with the principal to see if he/she has any suggestions. If you get some ideas & suggestions go for it. If not then I would not worry about it and move on.
At our school we do something we call duty free lunch. This is where we get a group of volunteers to sit with teachers classes while they enjoy a catered lunch in the teacher's lounge. We have not been able to do one in the last coule of months, due to other event planning going on and lack of volunteers. I brought this up at our board meeting last week. We have a teacher rep who sits in on these meetings. She is a very vital part of our organization, she helps plan events, etc and I consider her a friend of mine outside of school politics. But during this meeting she turned to me and said duty free was not a big deal, it was only 20 minutes of free time once a month and it didn't matter to her whether we did it or not. Now these things are very hard to plan. It takes about 10-15 volunteers and it's hard to find that many people free on the same Friday. So I decided to email all the teachers and ask them to let me know if they agreed with this. If so then I don't plan on stressing over this event anymore. I already know the event is going to be canceled because I only got a reply from 3 teachers. So maybe it isn't that important. But now the teacher rep isn't speaking to me. In fact, she is on car rider duty everyday and is in charge of calling students to their vehicles, she usually comes over to my window to chat for a couple minutes while we wait for all the kids to come out, but Friday she didn't even call my child to my car. I never mentioned her name in the email, I simply said it was brought to my attention by a staff member that duty free lunch is not serving it's intended purpose, which is to show our apprecation for everything our teachers do for our school and our kids. What do I do?? This has not been a good month for our PTO.