While a trainer is ALWAYS a good idea (one is never too "trained" to learn from someone else) in a dangerous rearing situation like this, some more background info would be good.
How old is the horse?
Is she greenbroke (new to riding)?
Has she been checked recently by a chiropractor and equine dentist? (Sometimes pain can cause a horse to lash out, so you want to check that.)
Does her tack fit properly, or is something pinching and causing pain?
Does she have good ground manners? (Does she get into your personal bubble or drag you around on the lead?)
When did she start doing this?
How (in great detail) are you cueing her to move forward?
How instantly are you lunging her to punish her? If there is any break longer than 3 seconds, she's not going to correlate her punishment to the rearing.