What helps, as a manager, when someone on the team needs early finishes for her son's therapy?

I manage a testing team. One of my engineers told me last week that her son has autism and his therapy sessions move to 4 pm twice a week from June. She asked, very carefully, whether she could leave early on those days and make up the hours at night. Saying yes was easy. I'm less sure about everything around it. Two people on the team have already asked why she 'gets to leave early', and I can't explain without sharing something that's hers to share. Our own daughter is a baby, so I have no experience of this from the parent side. If you're a parent who has asked for this at work, what did your manager do that helped, and what made it worse?