How far into her nap is she waking up?
If it's 30 mins, could be OT and needs some extra blocking out of stimulation, physical helping through the jolts.
If it's 40 or 45 mins, it could be not tired enough to go back to sleep (needs an increase in A...not sure what you're on now) OR could be that just needs help getting back to sleep but shh patt is too stimulating.
Perhaps try either shhing, but not patting. Or vice versa. My DS responded well to my rubbing / soothing his back very very lightly or just resting my hand on his chest. Comfort without any stimulation or activity, IYKWIM? They reach an age where ssh patt is too much for them and it's all bit exciting (or for my DS, sometimes annoying).
HTH. Let us know how you get on?
Charlotte