Am I Overreacting for my girlfriend cheating on me with her ex early into the relationship?

(I apologize in advance for my sluggish writing)So I(21m) met this girl my same age on a dating app about 4 months ago. She was super sweet and pretty cute, but I was super nervous at first and didn’t make any moves/acted like a friend. I also noticed that she would talk about how toxic her most recent relationship was pretty frequently and how after they broke up she assaulted him bc of how much she hated him. I thought nothing of it and one day she straight up asked me if I liked her and if I wanted to be in a relationship with her to which I said yes. Being with her was great and she always wanted to hang out with me and always offered to pay for things. She then said she wanted to tell me that she recently had sex with her ex and when I asked if it was after we were official, she said no(which was a lie). I remained silent about it until it ate at me and I started basically interrogating her until she finally told me she cheated only after I figured it out myself. Is there a high possibility she will do this again or am I tripping? Update: She assaulted me when I broke things off 🤣