She is only allowed to fly to her destination, not anywhere else. She notices that she is not where she should be, that she cannot progress to where she was told to go, and she careens out of control when her wings won't flap anymore, and she crashes.
The person she crashes into emits a slightly terrified yelp. He freezes for a moment in confusion and alarm, then scrambles away and turns to stare at her.
This does not help much with the confusion and alarm.
Apart from the unhappy mortal, her surroundings consist of a bit of clear ground next to a pleasant-looking if oddly-architected house. There is a lake visible in the middle distance, with a forest next to it; the forest curves around the house but doesn't come close, in a way that suggests it has been encouraged to leave the house plenty of room.
The crashed fairy can't yelp. Or exclaim in pain; she was allowed to fix her wings for the flight but she's still got broken fingers and a black eye. She cannot take off again; she could probably run away from the mortal, but she does not, it seems, have to; she scoots away from the heap of mortal and sits, cradling her injured hand and watching him.
He calms down over the course of a few seconds spent watching her; then he sits up and performs a quick, practiced sequence of movements that seem designed to check himself for damage. Flex shoulders and digits and limbs, twist torso back and forth, press on feet with hands. When that few seconds are over, he regards her with a mix of concern and curiosity and ventures a cautious: "Hello?"
Well, out of the range of possible responses to that, he thinks he'll go with...
"Um, do you need help?"
"I'm going to interpret that as a yes." He considers available resources. "In the realm of things I can get you quickly: food? Water? Painkillers?"
He goes into the house.
She isn't usually allowed to go wherever she wants, but she can in fact follow him right now. She does.
A couple of turns through the very mortal house, and they arrive in a very mortal kitchen, where her very mortal guide (who is a little shorter than she is - aren't mortals supposed to be large?) fills a glass with water and leaves it on the counter while he fetches a box of pastries out of a cupboard. (The kitchen is definitely built for people larger than this particular mortal.)
He extracts a pastry from the box and offers it to her with a thoughtful frown.
"This is very weird," the mortal remarks.
He puts the pastry in her mouth.
"Okay," says the mortal, picking up the glass and holding it for her to drink from, "something is definitely going on here that I don't understand. Multiple things that I don't understand are going on here."
He smiles wryly at the blink, and keeps holding the water for her. "Which first: painkillers, or attempting to communicate about the nature of your problem?"
"Second thing?" he guesses. "All right. You seem constrained rather than impaired..."
"I confess I am not oversupplied with theories about how that could come to be. But I would like to unconstrain you if possible," says the mortal.
"So. What do I know..." he muses out loud. "You have wings and you fell out of thin air and you weigh much less than I'd expect from a human of your size. And you can hear and understand speech and walk and sip and chew but you seem to be constrained from speaking and gesturing and feeding yourself...?"