Staying in the groundwork space until she can have the same results as you seems like a really logical next step. Learning how to be effective through lightness will serve her throughout her entire life as a horsewoman and prevent many good horses from getting dull or resentful.
Vet the horse to ensure soundness. Stickiness and lack of forward movement can be a soundness issue.
If sound, get your daughter and pony on a lunge so you can control from the ground. Have your daughter go without reins and stirrups and work on the rider’s position. Find out if she is using too much leg (causing a dull horse) or not enough by analyzing her seat. I still take lunge lessons after a lifetime of riding - we all need tune ups.
I’ll raise my hand. My old mare was wonderful, we had a great partnership. We competed together doing fun shows up to the .90 meter and going on trail rides, doing clinics. Loved her to death.
Two years into our time together, she broke her left hind splint bone. It took a while to rehab, but 5 months later I was back in the saddle and so thrilled. For whatever reason, though, Callie decided that I was no longer her person in the saddle. We had multiple vets out, checked everything, tried everything. She was fine for trainer and my friends - but when I got on her back, she just said, “Thank you, next.”
It was devastating, but I sold her to a kid down the road who was a less educated rider and they’re having a blast. We think she decided that she had enough to going on the bit and doing shoulder in - she would rather just be a kids horse, so now that’s what she’s doing.
Sometimes, and it rarely happens, but sometimes, it is just not the right fit.
This was definitely my problem. I have historically been known for making horses slow (they go, just really slowly). Couldn’t figure out why. I typically was given the jiggers and the speed racers to ride at the riding academy that I grew up in because I could get them to walk flat and not tank off.
As it turns out my pelvis has a slight issue whereby my seat bones were just slightly pointing the wrong way (hollowed actually) with a slightly braced back having the net effect of riding the handbrake. Using the pelvic clock device has been amazing for opening that up. Now I have control over the brace or lack thereof.