If you don't want to rear face her, then the Nautilus is a great choice. Our daughter will be 4 in April and is still rear facing, so its possible beyond 1yr and 20lbs. Its called Extended rear facing.
ANYWAY, a forward facing car seat is outgrown when one of three things happens; the child goes over the weight limit, the shoulders go over the top harness slot, or the tips of the ears become level with the top of the seat. The shoulders must be just at or below the harness slot for forward facing, if the shoulders go over the seat has been outgrown. Most kids will grow out of a seat in height long before weight. I'm just going to guess the seat she's in now is a Cosco Scenera? They ae usually outgrown in height around age 3.
The Nautilus is a great choice, she will be able to use the harness for many years and then use it as a booster seat.