Good that you pushed for the check and the blood test, that's one relief and can set your mind at rest!
It's not uncommon to have the leg aches at that age, and I guess it depends what she does in terms of exercise etc. as to whether or not they ache in the day.
A number of children in Ds1's year at school (Y3) have been experiencing leg pain issues; 2 girls who he dances with, one of whom had them so badly that she was taken to a physio, who has given her stretching exercises to do, to help encourage the muscles and ligaments to grow quicker to match the bones. The other one, poor thing, was overdoing it in dance class and tore her hamstring (luckily only a very minor tear).
DS1 himself hasn't complained of pain, but he's unbelievably tight in the legs - so we've been doing the stretching exercises as well, just to encourage his legs muscles/ligaments to stretch before his bones try to!
Things like:
Lying on their back on the floor, one leg out straight, the other bent to a 90 degree angle at the hip and knee. Hold the leg behind the knee and pull towards the chest, keeping the 90 degree angle at the knee joint.
Using a swimming noodle or other foam roll behind the knees, kneel down - this opens up the knee joint without damaging it.
Have the feet placed on a board that is set at an angle - heels to the floor, toes on the upper slope - helps to elongate the muscles of the lower leg in particular.
I've also been doing toe-touching with DS1, forward lunges (feet both pointing straight forwards, hips straight and leaning into the bent front leg while keeping both heels on the ground), and a few other things that are more dance-related (toe pointing, ballet positions etc.)
Hope some of these might help.