I commented about how I liked her pony tail and that was always one of my favorite looks for her, and her reply was "will you stop doing that already!" She told me the other day she was having a hard time with me being so nice to her all of the time. I'm sure it's making her feel guilty because she feels no compulsion to return the compliment.

She doesn't want to compliment your pony tail?

I don't think I've ever met a woman who doesn't like a compliment, although there are those who feel uneasy accepting compliments out of modesty. But if I go with the premise that women appreciate compliments, then I'm led to wonder if it's more about how you are expressing the compliments that affects her rather than that you're complimenting her.

It's difficult to say exactly why she's asking you to stop, could be feigned modesty, could be guilt, but if it's guilt, I'd not think it's guilt about not returning the praise. It may be more about that she's done a sh*tty thing that affected you badly, and there you are, still demonstrating appreciation of her through it all.

Reading through your post on the MLC confirms that, as she told you "would you stop being so damn nice to me, I'm treating you and (son) horribly and I don't deserve for you to be so nice."

So, since this behavior now is the "new, nicer" you, you've changed the dynamics around on her, and aren't giving her justification for her untoward behavior. She's struggling with that, it appears. She can't get you to get angry at her when she blasts you; out of frustration she simply demands that you stop being so nice!

I expressed some concern about this in my other thread as to whether I should stop or continue. Am I violating one of her "boundaries", or is she testing my fortitude and stamina to keep changes going?

She's going to continue to fight it, most likely, to try and get you back into being the guy she left, or she'll have to eventually change her reaction to accommodate the new nicer you's behavior. Given that, I wouldn't stop.