She's got it backwards. I've heard that more plump women don't feel the baby move as soon as a skinny woman does (makes sense, if you are skin and bones and the little guy starts kicking you, you are going to feel it a lot more then someone with a lot of padding.) Every woman is different, and she is probably just a bit worried if she hasn't felt the baby move yet.
I was almost 6 months along before I felt my first baby move. Every day at work, everyone kept asking me if I'd felt her move yet, and it got really annoying because I wasn't feeling her move. I'm pleasantly plump, so that was part of it. Part of it was just her. My 2nd pregnancy I weighed the same but felt my son move way more then I ever felt my first move.