I'm not sure wby they bad Orlin return as a child, but perhaps it was because they wanted to have an Ancient intervene in a limited way (at least enough to explain some plot points) and Orlin was the only Ancient they could task for the role, but they didn't want to reintroduce a real romantic entanglement for Carter.
Perhaps they just like to leave her bizarrely conflicted. Does she reunite with the Orlin child, or drive to the local high-school and seek solace in the arms of the Jack O'Neill clone child that Loki created? Perhaps a threesome behind Chuck-E-Cheese?
It could've been worse.
"Orlin. If a human brain isn't big enough, why didn't you come back as an Asgard?"
"Because then you'd just stare at my naked little Asgard butt, and I wasn't sure I'd be comfortable with that. Also, I don't like their little food cubes. Even the yellow ones."