Flipperruby30 said:

Sounds like shes had some kind of bad experience with saddle pads,saddles or riding in general.I think you need to go back to basics with this and build up confidence.Just start by letting her smell it,whether this be just leaving it in the field so she can approach it when she wishes,or holding her and offering it to her.Then,when she is comfy with the smelling,just gently rub her neck and eventually down her back without her spooking.All about positive experiences,like grooming is an enjoyment so incorporate that?And most of all,reward her through all the stages,even just little things like her standing whilst you touch the saddle pad,or she smells it.

Be patient and you'll get her comfortable.Maybe consult a trainer or behavioural expert?