How can I tell someone that they're heavy footed...?

Kind of a lot of background goes into this. One of my good friend’s girlfriend [Sarah] moved into the room above me. I don’t know her that well, but she moved in with a girl that I’m really good friends with.[Lisa].. They don’t really know each other and don’t talk much, but Sarah got assigned to the room (college dorm)

Recently I’ve noticed that I get woken up in the mornings, by Sarah walking. It sounds like she’s stomping around, but in reality it’s just that she’s extremely heavy footed. (she’s not a big girl either, if I didn’t know it was her, I wouldn’t believe it). Lisa has noticed it’s a problem and wants to approach Sarah about it. What is a good way for her (or me) to approach Sarah to bring this up without being rude?