That's odd. Maybe he knows the one line and can't beat anything else, even an 8 year old.
One suggestion- although avoiding mate is more important, in general try to avoid giving her too much unasked-for advice. People like to learn for themselves much more than from others.
My daughter has some interest in learning chess and I like to encourage something like that. Two weeks from now it could be a completely different story but for now she wants to learn how to play. So I am showing her some things.
Here is the funny part.
She wanted to play against someone on here since she knows I play here. So I set her up with an account for her to have some fun with. So we go to live chess and accept a seek.
I am watching her play and being a beginner she is making beginner moves. Well her opponent sets up a scholars mate threat. I tell her to move her knight up so she wouldn't have an immediate bad experience and lose interest since she is just beginning. Lets face it---getting checkmated on move 4 when you're just starting out can be a bit unsettling.
Next thing I know her opponent resigns as soon as the knight moved up. Resigning on the fourth move...
I check the profile and her opponent is 27 years old. My daughter is 8.
If he only knew...I just thought it was kind of funny.