Mab is not Murphy. Nor do I believe Mab will ever be Murphy.
Agreed, she isn't Mab... Hard to say if Harry and Murphy hooked up enthusiastically... Harry gave her a sock full of diamonds and a passionate kiss... Her eyes got big, so on his part, yes, her part? Not so clear since that moment, the two short stories about Harry since, not a word about her... Mainly Harry moving into Molly's old place, not a word about Murphy, then going to the zoo with Maggie, not a word about Murphy.... Yes, she might be in rehab, but that shouldn't keep her out of the picture if she and Harry were an item..
My guess is she may be staying distant so Harry and Maggie can bond, but then again one would think that Harry would want her to be a part of that...
We have evidence of Murphy's extreme independence, especially when she is going though a hard patch.. After Nightmare had gotten hold of her, she turned to the bottle, which worried Harry, but she refused all help saying she had to work it out for herself, which she obviously did.
This time around it is physical damage but there has to be a degree of emotional damage as well inflicted by Nic. Yes, it all turned out well in the end, the Sword of Faith was remade and we have a new Knight, but it could have ended very badly because of her judgement. She'd be the first I think to admit that she fucked up, and might want some space to work out the implications of that. Given what Harry has to work out, she might have unselfishly insisted that his daughter comes first. We don't know as of yet how her physical rehab is going, how quickly she is bouncing back, and how much of her former agile self will never come back.. If it is significant at all, Murphy isn't one who wants to be the object of pity, real or imagined so she might not want Harry around during her recovery... She is unpredictable, she may even resent Harry's expensive gift given her situation and tell him to go fish with it...
Or they are still very enthusiastically passionate for each other, just off page for the two short stories where Harry was one of the principles since Skin Game... However I still think it odd that if they were, her name wasn't mentioned once...