Back on topic...
I like Kendra. Sure, she serves a fairly predictable dramatic purpose in being the innocent kid who becomes Soji’s non-judgemental pseudo-sister but the role is none the worse for that.
From a characterisation point of view, I found her to be entirely believable as the kid of Troi and Riker. She has attributes consistent with both of her parents and carries the inevitable scars from the loss of a beloved sibling.
To be honest, it felt a bit unnecessary that the writers had to give yet another set of characters some sort of profound trauma — it gets a bit tiresome when they try to do this to absolutely *everyone* we meet in the show. It’s just clunky and heavy-handed writing if they feel the need to give that extreme level of angst to ALL the characters in the show. They could have just made Thad a few years older and have had him be away at Starfleet Academy (or whatever), with Kendra missing him while he’s away.
The whole “rare-sickness-and-died” but “could-have-been-cured-except-for-the-ban-on-positronic-matrixes” all felt slightly OTT. To be fair to Frakes, Sirtis, Stewart and Lulu Wilson as Kendra, they really do make the most of the story and script as written, so I can’t fault them with that, but that part of the backstory felt particularly overblown.
Overall, however, a great episode and Kendra herself is a very worthy addition indeed to the extended TNG family.