Welcome to the forum! Sounds like you and Maya are off to a great start. It's rare for females to get to 12" but it does happen. At her size/age, you probably shouldn't notice much growth, unless you actually measure her. It's a good thing that turtles are allowed to grow slowly.
I'm looking forward to what you come up with... a build thread will be nice

As for food... she might just be holding out for the good stuff. A last note, if you found her crossing, she might have been looking to nest. So might have had eggs and should be returned if she's wild and was just heading home.