I would be very upset in this situation as well. It sounds as though she is looking for any reason to be upset. It's soo frustrating when someone decides to be upset 'on your behalf' because it's never really on your behalf.
I agree that perhaps this is one topic that is too triggering for you to have with her. You could try the broken record approach with this one, if that is what you decide. Just keep reminding her that you aren't okay with this issue being discussed. If she is an argumentative person, she may try and argue back about it, but if you keep repeating the same sentence to her, she will eventually get the message, or at least get annoyed enough to let it go. The more reasons you give an argumentative person as to why it's not a good topic, etc, the more ammo she will have to argue against you and it will just exhaust you and get stress levels up.
I'm sorry she can't be more supportive for you. I hope that you have people in your life that are supportive in the ways that you need!
xo
IJ