Not sure. She has one of those fiber boxes with branded router provided by the operator. I should try to access it next time I visit her - it might have some sort of parental control.
Probably does, but if she is renting those, you should do her a favor and replace them with something she will own and that has parental control. Or maybe change the DNS servers to one in your control (not sure if that will work with the encrypted DNS though that get pushed onto you by Firefox).