Daughter knee has deep bad pain when putting weight on it or bending it, never been broken & doesn't do much sports what could that be?

It could be related: to a condition called patellofemoral syndrome, which occurs when the upper and lower parts of the leg are not aligned properly, putting a stress on the knee(s). This is very common in teens,especially girls. However, she may have had an injury that she doesn't recall, so I would recommend having her see her doctor or an orthopedist to be diagnosed properly.