Sarcasm can be really hard to deal with. I had a situation that demonstrated the varying impact of a sarcastic remark pretty well and wonder if it may lead to a technique you could use.
The scene was lunch at a restaurant with my parents and children. My dad squeezed my (overweight) mom's upper arm, looked at S18 and said "Look how strong grandma is getting".
It was obvious to me (and my mother) that this was a sarcastic way of pointing out how fat mom's arm was. Mom was apologetic but hurt ("I know I need to lose weight". I was stunned and angry, both that Dad would say something so hurtful and that he would do it in a way that involved S18.
It took me several days (and some coaching from members here) to talk with S18 about the incident. I asked him ":)o you remember when grandpa squeezed grandma's arm and said "Look how strong grandma is getting"? What did you think about that?"
S18's response - "I thought grandma must have started working out and grandpa is proud of her."
So I took the sarcastic comment as {I feel} it was intended and ended up hurt and angry. S18 took it at face value and came to a conclusion that probably would have shamed his grandpa. If S18 or I had said to my mom "Sounds like you've been working hard and grandpa is proud of that. I need to check out these muscles. Wanna arm wrestle?" I think my dad's motives would have been properly revealed and/or diverted.
I don't think you are being too sensitive (otherwise I would need to think that I am too sensitive

), but I do think that responding with hurt only rewards and encourages the behavior. What if you tried reflecting back to her the sarcastic remark minus the sarcasm and went on face value? Choose to take the sting out of the remark. If the goal is to hurt you, then she will have to acknowledge and do so more overtly.
If she calls out the behavior, you can be honest and say "There are times that your comments hurt me because I feel they are sarcastic. I'm working to make sure I don't read anything into your tone that creates hurt and anger in me and conflict with you. When those situations come up, it helps me to repeat back your words and what I think they mean without my perception of sarcasm to make sure I'm understanding correctly.
Have any sarcastic comments that we could role play this type of response with?