17yo is babysitting 11yo regularly now and starting to ask why we "go away so much"

F44 dh 47, two kids 11 and 17. as the older one has hit an age where shes safe and responsible to watch her younger brother for an evening (and she actually enjoys the small cash flow), weve started using her for our friday and saturday nights instead of a sitter. saves us money, kids are comfortable w each other, on paper great. except. shes 17 and shes paying attention. she has noticed that since we stopped using paid sitters and started using her, we go out roughly twice as much as we used to. like she said to me last weekend "why have you guys suddenly become party animals, you used to be in bed by 10 every saturday". and shes right!! when we had to pay a sitter 60-80 quid a night we did the math. when its a tenner to our own kid we are out the door. so now i have two things to manage simultaneously which were both easier when she was younger. one, the cover story (where are we going, etc), and two, the simple fact that the FREQUENCY of us being out is now a noticeable change in family rhythm that didnt exist a year ago. also and this is the bit i find genuinely tricky, shes also a young woman herself now. shes had a bf for 6 months. shes navigating her own social life. so theres this weird sense in which we're both "people who go out now", and i feel her watching me and dh w slightly more grown up eyes than i was ready for. how does anyone manage this when your live in sitter is also your half adult child. do you just go out less. do you go back to paid sitters even tho the kid is capable. do you... idk what im even asking, just need other parents who have been here.