How do you stop a pony jumping out of her field?

My 13.2hh 23yo retired jumping pony has recently had laminitus for the first time and now has to live in a fenced off area of the field to keep her off the lush gr (which is awaiting farmer to cut for hay) She is out with my horse and there are no other horses in the fields. It is electric fencing and has the highest stakes I could buy, the fence stands at 4' 6''. Problem is she just trots up and pops over it like its nothing and then eats as much lush gr as she can before she will eventually let me catch her and put her back in where we start the process again. Any ideas what I can do to deter her?