All lop breeds, with the exception of the English Lop, have a ridge of cartilage on the top of the head. This area is commonly referred to as the crown. The development of the crown is what determines ear carriage.
Ideally, the crown will be wide in two directions - from side to side and from front to back. If those proportions are achieved, the ears lop well and the rabbit loses ear control.
Sometimes those proportions are thrown off, and one or both directions are narrow or undeveloped. When this happens, rabbits will have varying levels of ear control. Some ears stand almost vertical, others and halfway ("airplane ears") and others will carry one up and one down.
Age also determines ear carriage. Young lops often go through growth spurts where the proportions of the crown are askew. Obviously during those times, the ears can get kind of wild. Every genetic line develops at different rates, so rabbits go through these stages at different times.
Based on your rabbit's age and current ear carriage, I suspect she will always have a bit of ear control. However, she may surprise you. In my experience, crowns seem to continue to develop until the rabbit is 2-3 years old. Usually by 6 months old, you have a pretty good idea of how severe their carriage may be, and by 1 year old, the ears start settling into their final position.
Some rabbits develop much earlier and drop their ears within the first couple months. It just depends.
