I think I'm being gaslit

I turned 18 back in October. I had a big party and my older sister threw a party for me. We are 14 years apart so we've never been close but we finally are starting to get there. She and her friends supplied us with alcohol and the party was fun for the most part.

Well now she's in trouble because she hooked up with one of my friends who was 17. Where I live 17 is age of consent but they have to be within 3 years of each other.

When I saw them making out I pulled her to the side and said "Hey. He's 17. Just so you know." She said "Oh shit! Thanks for telling me!" But still went up with him to her room.

Where I feel like I'm being gaslit is she is facing a statutory rape charge now and her defense is she didn't know his age and she wants me to testify that since I told her his age. However, I know for a fact I told her his age before they went up to her room to have sex. I pulled her aside when I saw them making out.

She's telling me I'm mistaken and I was drunk so I clearly don't remember but I told her it after. Yes I was drunk but I know when I told her. I saw them making out. I pulled her to the side. And then I saw them go upstairs after that.

She's trying to say that I never saw her and him making out and I didn't pull her to the side until I saw them come downstairs.

I know it didn't happen that way and I'm not gonna lie in court for her. Plus if they got done having sex and that's when she found out why would her response be so nonchalant.

My mother is telling me like I just don't remember it correctly but I know what I said and when I said it and I'm starting to feel crazy!

Now my mom is saying if I don't go up there and tell THEIR truth because it's not my truth then I can go live with my dad. I love my dad and wouldn't mind but I'm sad it's coming to this.