Boyfriends daughter doesn’t have a sleeping schedule

My bf and I recently got our own place we both have a child from previous relationship.. My son is 5 & his daughter is 7 due to Covid they are both not in school but my son does attend daycare mon-fri 7am-5pm I am very lucky to get childcare and I wouldn’t want to lose my spot because of this reason.. My son is on a set sleeping schedule he’s usually in bed by 9pm but his daughter on the other doesn’t go to bed till 3-4am!! I cannot tell her anything because she tells her mom everything & that’ll cause major drama between her & my bf. There were a few times that I don’t take my son to daycare because he stays up with my boyfriends daughter, now her mom was Covid positive 2 months ago & has not seen her daughter since, she’s BEEN cleared from the virus for quite a while now, shes been using that as an excuse to not watch her daughter. This honestly upsets me because her mom is all over social media having fun while I’m here stressing. I can’t tell my boyfriend anything because that’s his little girl.

Any advice? I’m honestly super stressed out about this