Sounds similar to my situation, OP. Very different background to my inlaws and my DH was like me, so different to his own parents, which made things strange and still does to a large degree.
But, actions speak louder than words, so they say.
They really didn't know you as well as they do now. You've shown that you're resilient and loyal and probably not the person they thought you were and maybe your MIL had the good sense to see that and embrace you.
Most don't overtly apologise, through words, but instead by trying to atone through actions. After all, if she apologised but did the same things, you wouldn't accept the apology, would you?
Maybe see her actions as the apology you deserve, if you're so inclined.
In any event, I'm glad things are easier as far as the family coming around to see you as the person you are and not the person they assumed you to be.
Some people never achieve that status with MIL!