As someone who knows a lot in this space, I'll give you what I believe is 99% the case in situations like this:
She is assessing your value because it determines her value.
If you are doing poorly in life, she made a good choice and she can rest soundly at night.
If you are doing well... You've moved on from her, maybe have a better job, a hotter new wife, happy kids... She may feel like she messed up...and her biology doesn't like that.
Women behave this way with exes because they have to know how things stack up in the tribe. It's the same reason they follow celebrity gossip.
On top of that they have a strong drive to be romantically aligned with the highest value man they can secure.
More personally: don't read too much into it, and if you are doing well and she does reach back out to you, never, ever take her back. A cheater will always cheat again, and that is a boundary no one should cross.