Should I forgive my cousin who tried to ruin my relationship?

I (F25) have a boyfriend (M25), I had a stressful situation few days ago, related to my family and relationship. My cousin (F19) texted my boyfriend, my boyfriend told me about her text, as she continues texting, giving him compliments and asking about his job and telling him hers. I knew about it all as my boyfriend kept telling me, we thought its not cool and I talked to my cousin about it, to which she was being ignorant. Me and my bf blocked her. I texted my aunt ( my cousin's mother) and told her to talk to her daughter. As I found out while talking to my aunt, her daughter lied about it all to her, told her that my bf is the one who started the conversation, and that she was trying to praise me to him. I was shocked about it and i said its all a lie. My bf has all messages and there is no way to hide that she is lying.
After all this, after feeling so hurt by my cousin, my mother keeps telling me that its rude to block her, I am really hurt and I don't need her as my cousin, as she is trying to ruin my relationship and spreads lies about my bf in family. My mom says that I am so rude and that I should try to talk to her as an older sister ( which I tried and got ignored). She also blocked my brother in her social media I don't know for what reason.
I think the reason my mom wants me to forgive her is that she is family member and its not nice to have stress and arguments with each other. But on the other hand I feel hurt by her actions towards me, I believe if i forgive her she will be even worse. Me and my bf trust each other, but I don't want stress in my relationship because of her.
PS. me and my bf are dating more than a year, and my cousin too, has a bf,
TLDR; Should I listen to my mom and forgive my cousin who tried to ruin my relationship?


Source.