I had my first fusion in 2001 (I was 22 years old). L5-S1 was fused; had 4 pedicle screws placed with vertical rods connecting them. They did take a block of bone from my iliac crest - that was the worst part of the recovery. The back felt better long before the hip did.
My second fusion was in 2004. This time they fused L4-L5. The S1 pedicle screws were removed as that fusion was solid and they weren’t needed. They used the existing L5 pedicle screws, added screws to L4 and placed vertical rods and a horizontal crosspiece connecting the center of the rods. This time they removed the L4-L5 disc and placed a block of cadaver bone in it’s place.
Recovery from the second surgery was much quicker. I’ve had no problems since, I have excellent mobility (can still touch my toes while keeping my knees straight!), and I can ride without any problems. I do mostly dressage work with my OTTB who is prone to “Thoroughbred Moments” when he thinks something will jump out of the trees and eat him 
I do a lot of routine work around the house; gardening, bending over, waxing the cars, stacking firewood… I might be a little sore after waxing 2 cars in a day, but who wouldn’t?
I do have a patch of permanent numbness on the outside of my right thigh; that’s been there since the first surgery.
One more thing: My first surgery was done by an orthopaedic surgeon who specialized in spines. My second was done by a neurosurgeon. If possible, use a neurosurgeon. My second surgery was 8.5 hours long compared to the first (3 hours) and I really feel like the neurosurgeon was very thorough and meticulous where the ortho was just concerned with finishing the surgery.
Best of luck to your DD and please feel free to PM if you have any questions.
Taryn