Whether they reject you for looks will be down to the specific airline. But you must be strong enough to operate the "worst case test sample" cabin door mechanism. They actually test you for this because it's a regulatory requirement. Many skinny (size 6 or less) women have had a problem with this, so if your upper body or arm strength is lower than typical you may want to pump some iron in the gym to build up some biceps before applying.
PDR