I gotta say while I see all the controlling stuff people are mentioning, what stood out to me was the "extended sleepovers". This kid is regularly spending multiple nights at a time away from her parents' house to the extent that the relatives just assumed it would be fine to take her for a couple weeks? That honestly sounds like the opposite of a controlling parent to me. Like, either LW is *obviously* abusive such that the husband's family are teaming up to keep the daughter out of the house as much as possible, or this whole family is incredibly laid-back about trading their kids around compared to most families I know of. (Or both.)

LW, if your kid is regularly spending a week at the cousins', it's perfectly reasonable to cut back, most kids don't have weeklong sleepovers on a regular basis. Unless you *are* abusive and controlling, in which case you should agree to let her go there as much as she wants.