It's definitely possible. That would certainly be an interesting twist, considering everyone has assumed that it was Lady Tremaine up until this point. I just don't know exactly what Drizella's reason or motivation for casting the curse would have been. And if she did cast the curse, then why would she have allowed herself to remain under her mother's thumb in the new reality? No matter what, that would be a cool thing for Adelaide to get to play.
Spoiler:
I do see the parallel with Regina flirting with Charming, but... I just got the feeling that Ivy's feelings are genuine.
I could be completely wrong, though.