I was in the same position as you a while ago, though the time scales were slightly different.
My ex broke up with me, and was with another guy (a mutual friend) before the week had even finished. They were together 8 months, from January to early September. Most of that time was hell for myself.
In that September she started texting me (after 3 months of no contact at all - it was the uni summer hols, and the contact before that had been abusive from both sides tbh) asking for me back, coming out with similar statements as you're getting, "It was all a mistake", "I felt I had no choice to get out of it but I wanted you back" , "I was lonely, he meant nothing" etc etc.
I said yes to having her back.
The result was 5/6 months of sort of sort-of normality being back together. However, I now realise during the whole time, we never addressed any of the issues occuring from the circumstances and time apart, and were pretending they didn't exist. When I did ask questions regarding the issues, I never had a real answer given and she'd make out I was being unreasonable for asking.
It all blew up when I found her texting her new-ex the exact same lines she had fed me to get me back.
It may not be the same for you, but from my own similar experiences, I say stay away, well away. It hurts to be apart, it's hell, but once you've been treated this way, you'll never trust her again, and maybe for good reason.