should I let it go, or beat her ass?

She came home at 3 am last night an it was Valentimes day! I knew what was up but she doesn't have a boyfriend that she has told me about yet. She wasn't drunk or high believe me! I wasn't the best teenager growing up so I know what signs to look for. Plus her older brother tried to be slick and do that before. I knew the second he walked in the door! Anyway we have cameras outside our house bc we have a car radier going around. I seen her get out of a car I recognized from her best friends house. I thought that's who she would of been with but why wouldn't she tell me? I called up her best friends mom and she said that my aughter wasn't there last night, and her daughter ( my daughters best friend) is with her dad in Florida bc her grandma passed away. I was extremely confused, until I remembered that her best friend has a step brother who I never quite liked because he always gave me an off vibe. So I then called her best friends mom back and asked her if her step son had been anywhere last night and she said not that she was aware. So while I'm sitting here trying to find a way to figure out how to find out who the hell she was with last night and why the fuck they were out so late, I hear her shower in her room start. You already know my paranoid ass was up then stairs and in her room searching for her phone in less than 30 seconds! Lmao I found her phone and in our house, for as long as I pay for that phone, I pay for the password too. So I knew the password and I got right in. I didn't go through anything except her texts, I opened up one that's name was just emojis, and I read "Did you get in with out getting caught??😂😂😂" and my daughter responded "yeah 😂😂, but I'm sorry I didn't want to do anything. I just didn't feel ready, I want to wait a while before we do that." And I got PISSED. I was also propos of my baby girl for saying no, but hell fucking NO! She snuck out of my house with the intention to have sex, but then changed her mind? What if she didn't! When I heard her shower turn off I closed out all of her apps and turned off her phone and left her room. Should I keep acting like I don't know what's up and wait for it to happen again, or beat her ass now?
*UPDATE: she is 15, turning 16 in June 
*also, when I say "beat her ass" I don't mean I'm going literally kick her ass. I mean I'm going to make her life HELL so she knows not to try that bs ever again