frankly speaking, i wouldn't recommend u shoot from the feet, esp wide angle, the legs will look big big & the head small small. unless u deliberately want it that way for comical or abtract effect.
if u must lie her down & want to emphasize her long legs, u may want to lie her straight on her side with her front facing u. If she is tall, her long physique will show when u shoot full-body in landscape mode (since she is lying down).
If not, u can shoot her from a low angle with her standing. will make her look tall.
also, clothes come into play. if she really has long legs, wearing a very short pants will enhance the fact.