Does it happen every time she gets up? Any differences when sleeping on floors/carpet/dog bed? Any other time it happens?
She could just have slept on the muscles the wrong way
Or her leg fell asleep.
A vet visit is always good if something concerns you just to be sure
Panosteitis generally shows in the front leg(s) before the hind legs, but an xray would help determine if this is the case
If it was a torn ACL there would be very noticable limping usually also holding one leg off the ground completely
Could be just a sprain, depends on how often it happens and if it occurs at other times as well ie after a walk.
Hip Dysplasia generally shows pain when pressure is put on the hip area, so if she fell asleep while you were checking her hips I'd say no to that one.
This can also be determined with xrays, it can be an inheritited as well as degenerative disease so unfortunately milliions of dogs every year are diagnosed with the disease.