@Kie1 Possibly she is booking under her child's account.
"Dear <guest>, we are looking forward to hosting you on <date>! I just wanted to check in with you about one thing: you noted that you're coming to town for your child's graduation, but Airbnb tells me your i.d. indicates you're under 25. So unless your child is extremely precocious it looks like maybe we have some kind of mix-up. 🙂 Third-party bookings are not allowed by Airbnb's terms of service and as a brand new host I just want to make sure all my i's are dotted and t's are crossed. May I ask you just to confirm that you are <name> and you will personally be staying with us? Thank you!"
If she says she's not then ask her to create her own account and book using that.