Ex’s sister commented on my ig pic

I broke up with my boyfriend a couple days ago because he cheated, it hasn’t even been a full week. I just posted a pic on Instagram and his sister commented “sis 😍😍” she’s never commented on a picture before 🤨 idk if it’s a scheme just to see what I’ll say or if she just doesn’t know if we broke up which I highly doubt. Should I just ignore it? Or would y’all reply thank you? I don’t have a problem w her at all. But I don’t plan on getting back w my ex so I don’t wanna reply if it’s a joke from both of them just to see what I’ll say. Am I thinking too much into it? 😭