Went to DD2's 15 mo check up and she basically didn't gain weight since her 12 mo appointment

I was super surprised since she is a great eater. And even though she's very active, dr said there should still be some weight gain in 3 months...

We are going to try to up her fat content with food and she will go back in 1 month to do a weight check.

Should I be concerned? I was so surprised by this, and now feel so guilty like I must have missed something?!