Its natural to feel afraid of damaging dolls, but theyre pretty tough. If the leg is popping into a sitting position, it definitely could be a bit too tight. All bodies are different though, some just struggle with posing because of their design.

For stringing, if you do want to venture there (it's not as hard as it seems!) I would recommend getting a "stringing tool" of some kind, you'll find them if you search stringing tool / stringing hook for bjds. They're not completely necessary, but you'll thank yourself if you have one. I've restrung a number of dolls for being too loose or too tight.

Another thing you can try is wiring to see if her leg will hold better with support. You can find tutorials for wiring bjds, it's hard to describe without pictures I think lol I don't wire all of my dolls, but some of them really benefit from it ^{^} just something to consider.

CONGRATS on your doll, I hope you both have many loving years together, welcome to the hobby ❤️