If I could change something... I'd explain a few of the plot points better. There were some that just seemed too convenient, brushed off with a half-hearted attempt at explanation that didn't satisfy me (spoilers, highlight to read: like when Margherita could suddenly perform magic, explained away because she prayed to the Goddess, and so conveniently snoods were turning into nets and what have you) or stretching the bounds of credulity until they snapped (spoilers: Margherita not realizing she was pregnant — with TWINS — until she was giving birth??? Seriously? And the witch didn't realize either???).
There was also a central element in the original Rapunzel tale (spoiler: Rapunzel's healing tears) that became almost an afterthought in this retelling, and I didn't like the way that it was done here. Maybe the author was trying to turn this element into something more realistic, but it just ended up making both Margherita, and especially Lucio, look foolish. Spoilers: his eyes were dried shut with blood, so he thought he was blind, and so did Margherita when she saw him (but really he just needed to wet his eyes so that he could open them again). I mean... huh?
If you haven't read it: and you're looking for a mature, dark, historical take on Rapunzel, you're going to want to read Bitter Greens.
If you have read it: what did you think of the reveal at the end? I wasn't surprised since it had crossed my mind, but I still liked it because it made sense in connecting the narratives together. I also enjoyed the allusion to another version of Rapunzel and its author, and how Forsyth fit that into her retelling.
Just one more thing I wanted to mention: I thought one of the ending scenes — what really should have been a higher-tension moment — fell short. In particular, I just didn't buy the change that happened in a certain character; it happened too quickly and without (to my mind) sufficient motivation. Spoilers: Selena suddenly repents, and I wish we had seen this from her perspective; it would've helped to have been inside her head, because as it was, I didn't understand what was triggering this apparent change of heart, and so I had a hard time believing it was genuine. Not to mention, Margherita and Lucio let her go and blithely expected she wouldn't do any more nasty stuff (without any guarantee), which hardly seems smart.