Yes, some incentive system is fine. Practice makes perfect, as they say, and the more she can behave in a different way the more easy it will become.
Def. not an abuse issue.. she is with me 24- 7 ..What can I do to help her through it if it is that sensory issue??? Is it ok to bribe her with fruit roll ups??
There is an outside possibility that this reaction is emotionally-based, and it invites an evaluation by a mental health professional. Is she otherwise OK from an emotional health perspective? Do you have any idea why she might be troubled by clothing coming in touch with her genital area? Is there any suspicion of her having been abused?
It is more likely that she displays some tactile defensiveness that causes her discomfort while wearing certain clothing. If this is the case, an evaluation by an Occupational Therapist (the discipline responsible for the evaluation and treatment of sensory integration functioning) would be in order.