Fantasy/paranormal/romance, third book of trilogy with protagonist an invalid princess (fae?)

[Malmaison]

I was reading an awful lot of series in the fantasy/paranormal romance genre a couple of years ago and now I’m having trouble distinguishing details and telling them all apart. (Especially since I tend to binge read!).

One of of them was a series, I am pretty sure a trilogy, where I liked the first books in the series well enough but preferred the third. So the basic plot of the earlier book was that the human had to pose as an invalid princess in another realm because they were actually lookalike sisters ... I think maybe there were three sisters, one for each book? ... but our h in the first book was much tougher and stronger than the ‘weak’ princess she was pretending to be. However the book I really enjoyed was the last one where it swapped protagonists so you got the weak invalid princess learning to stand up for herself and kick enemy butt. I read it on Kindle probably in about 2014-2015 and really can’t remember much else, except that I wouldn’t mind reading that third one again! Can anyone help? It was not Young Adult.

[Lobstergirl, au gratin]

Malmaison, are you still looking for this or did you find it?