Our Leos fit true to size! We recommend staying in whatever size of clothing they regularly wear. If you still aren't sure- measure the Trunk Girth first and check it against the size chart. Then, move on to the chest and waist. If the measurements are 2 sizes off of what she is measuring in the Trunk Girth you might want to consider a custom Leo for a perfect fit. If custom isn't your thing, then order what her trunk girth size is knowing it might not be as snug in the ares she is measuring smaller in.