"I realize that the 10 min's is trivial"
Yeah, it's trivial.
Compared to how monumental losing her job would be.
"but my argument is that that it isn't legal"
Doesn't make a difference whether it is or it isnt.
She would be foolish to make an issue of something that trivial.
How about this as an alternative.
She comes in exactly at 9 AM and it takes her 10 minutes to get herself in order to where she is actually productive. It takes everybody about 10 minutes from the time they get to work before they actually get to work-ING. Would you rather she be docked for the 10 minutes she's not productive?