ICloud merged photos from 2 iPhones

I have an 11Pro Max, and my 11y/o daughter has my old 8+. They are both on my apple ID. Yesterday she toggled on the iCloud photo storage because her- my old- phone was getting full and needed some more space. The unfortunate result is that we now both have each others photos on both devices. Unfortunately, I have almost 20k picture and video from work I need to keep. Is there any way to undo the merge now that both are one on our icloud? I know its complicated by the facts that its all under my ID and that a large amount of the photos where originally taken with the phone she has now. Going fwd I want to find out if theres a way to create her own ID that I as a parent can oversee and be financially responsible for. But, until then i need to undo the mess a simple toggle created.