AIO about my ex texting me after 2 years

Hello hoping this is a good one to post, but a few months back my ex contacted me (20 F) randomly on Instagram. The last time we talked was 2 years ago and a few months, I don’t know the exact date but forever ago. Late at night around 4:00 am I got a text, saying how sorry she was for being a B. She then proceeded to text me back very fast and consistently. I diverted the conversation to the fact that I’m engaged now and she said she was to. So why in the world did she send me a message. For the last few months I’ve been wondering why she did this, not only is she engaged but if it was me I would never apologize if I’m getting married I just feel like I need this off my chest and some opinions.