Sounds like a lot of fun! My daughter (10) and I are currently sharing a horse, so she does a lesson for about 45 min. then I hop on the horse and do mine (instructor comes to our barn). Luckily our horse has endless energy! Planning on a second horse in the summer.
I've had horses before, but am more or less a beginner, esp. at English (was trained Western in my youth) whereas my daughter has been taking lessons for over four years. She loves telling me what I'm doing wrong and encouraging me to improve (mostly by laughing at me ;)! We laugh a lot and have fun. But she also takes group lessons with kids her age on Saturdays.
She has done summer camps, but they're always for kids. I've never heard of a mother/daughter type camp, but it sounds awesome. Hope you find one!