I love jumping I find it amazing.
I jump 4'3" on my horse, and I love it.
If your trainer thinks you should go higher you should go for it, s/he wouldn't ask you to do it if s/he didn't think you were capable. I think that you should go for it, the higher the jump the more rewarding it is, but don't push yourself. Take your trainers advise, you'll love it.