This situation isn't hard to figure out friends.
First Adele didn't accept Hex's proposal because she was still unsure of his role in her death from the original timeline. It was only recently she found out about his situation that she could determine that he wouldn't have had a hand in her death and only then did she accept his marriage proposal. As bad as her situation is, it actually isn't that smart to just runaway with a guy she's known for a hot second just because he's nice... And hot. Maybe once he made a million sandwiches for a 2 person picnic, but not before then.
That goes to why she waited so long... Well, consider that even if she did run, Hexion not withstanding, she has nowhere to go and no one to run to. Her "family" has kept her isolated and again, only recently because the situation in her life has started to change since the hunt has she thought to seek out a childhood friend who is doing much better for himself. If he hadn't been told that she was dead (I think? Why can't I remember) she might've been rescued sooner. Also, having Hexion pull her from a bad situation, instead of her leaving, ends up reading much better to more neutral witnesses (in this case the staff, who I know are complicit but rumors travel quick). If you've read The Villainess Lives Twice, that's pretty much what happens there, where the ML pulls the FL out an abusive scene. (Tia is a more interesting FL, but Adele isn't supposed to be an evil mastermind so that might be a factor.)