Long time bird owner here. Budgies, cockatiels, and African grey parrot.
For starters the pet shop owner sounds like a moron. So now that’s out of the way…
If your DD wants to tame him she needs to start out slowly slowly by introducing her hand into his cage. Just sit with her hand in the cage very still, and when he flies around just keep still until he settles.
Once he’s settled just sit for a bit longer. Repeat until introducing her hand no longer makes him flap around madly, then once he settles she can gradually bring her hand closer and closer to him.
Bring her hand close to him but lining up with his perch, so eventually once she’s really close she can put her finger next to his claws and encourage him to sit on her finger.
Once she has him used to going on her finger in the cage she can gradually move her hand closer and closer to the door until he comes out.
He likely will perch somewhere, that’s what they do. But she should then be able to bring him back to the cage by encouraging him back on to her finger.
The more he becomes used to her, the more she will be able to do such as stroke his chest etc.
Remember that she is about.a thousand times bigger than a tiny budgie, so to suddenly have this human looming over him is likely to make him even more nervous as he doesn’t know he’s not about to become dinner.
PS: I used to live in Namibia and we used to get love birds in our back garden. I would never ever buy them.