I have no answer to your dilemma, but I have a similar situation.
One day an entire litter (?) of ducklings showed up in my yard, eating out of my ground-level birdfeeder. I live close-ish to a river, but far too far (& predator-filled) for a mama duck to walk from. I knew nothing about ducks at this time, and thought - oh no, someone lost their ducklings. I managed to catch three of them. One died (he got stuck in the fence, unfortunately) but two survived. I named them Thelma & Louise.
They are definitely Mallards. At this point, I figure some neighborhood kids (who have since moved away) scooped them up from the river and brought them home, only to be told they couldn't keep them - so they just dumped them. Even though they are likely wild Mallards, I don't feel bad about keeping them - it rained that night, and I'm sure the rest of the litter I didn't catch died.
The drake - Thelma - has always been content to be in captivity. He does not attempt to fly away. He knows where his food & bed is. The female - Louise - has always acted "wild". Where Thelma would snuggle if you picked him up, Louise will attempt to chew a finger off. She likes to fly, and I allowed it (inside their pen) - until she started hurting herself with her bad decisions, and then I started putting up more bird netting to curb high flight.
One night Louise got out of the pen. Tore through the bird netting and flew off into the sky. Thelma did not try to follow her, even though her absence clearly scared him. I thought - Louise is going to find the local flock by the river, and I'll never see her again.
Nope. The neighbor - barely a couple hundred yards away - called me and asked if I'd lost a duck. She had flown towards them as they were walking their kids home from the bus, just the weirdest sight they'd ever seen. The problem, as Louise was quickly finding out, is that flying "runs out" when you're not used to flying distances. She wasn't able to keep herself in the air and eventually ended up crash landing into a bush. The neighbor scooped her up and brought her back to me.
This situation clearly traumatized her, because for a long, long time, Louise stopped trying to fly. Went from "always flying as much as the pen allowed" to "feet never leaving the ground."
Now it seems like she's forgotten - or simply willing to give it another go. She's still an escape artist.

But my perspective on her has changed - before, I thought, well, if she gets out she can choose her own life. But now I know if she gets out, she'll die. She does not have the skills - or the muscle - to survive, flighted or not. It is my responsibility to balance her mental wellness - the ability to engage in natural behaviors, which is an important & well-documented aspect of animal care - with her safety.
Ultimately, I want to build a flight cage for her. A big hoop coop with some serious security. And some beefy predator protection, so if she wants to sit her dumb feathery butt outside at night she can do so.