I think my mom touches me inappropriately and it makes me sick

Ever since I (17f ) have been through puberty my mom started touching my chest. I don't think she means it in a predatory way, she likes hugging me and physical affection in general. We would just lay in bed and suddenly grab one of my... yk

For a very long time I thought it was normal bcs she's my mom and I thought all moms do this. A part of me still thinks I'm overreacting but it makes me sick to my stomach.

This morning she did this again. It was so unexpected. We were laying in my bed and all of the sudden she touched me like this again. I told her to stop bcs it made me feel uncomfortable (I must admit I shouted a bit) and she seemed so offended by my reaction. She said I was overreacting bcs she's my mom and she has the right to do this.

I'm at a loss rn. I wanna explain to her calmly why this bothers me but she has the tendency to victimize herself and this discussion would do more harm than good. Both of us would end up lashing out at eachother. I can convince my mom that I need to go to therapy again (bcs school starts soon and I can tell her it stresses me a lot) and tell them abt my mom's behavior. But I'm really ashamed to talk abt this. I barely explained to my friend what I'm going through but I'm scared he's gonna judge me for it. I don't have any proofs this happened and I never brought up this subject so it seems out of nowhere