Well, I suppose it depends on her
instagram aesthetic
Satuli canteen - blueberry mousse (this one I have actually seen many instagrams of, usually a boomerang of the moment someone cuts into it with a spoon)
all of the special, seasonal, whatever cupcakes around WDW. an example list:
http://www.disneyfoodblog.com/2018/...ou-eat-all-14-of-disney-worlds-best-cupcakes/
at the edison in disney springs, the "lollipop tree" for dessert (though i don't exactly recommend the food here)
there's those considered iconic or classics -- mickey pretzels, mickey waffles, mickey bar, mickey ice cream sandwich, turkey leg, dole whip, etc.
most of the dishes at signature restaurants, appetizer/entree/dessert alike, will be very instagrammable.
all of the desserts at Flying Fish!
the dessert called La Sphere at monsieur paul. although it is not really all that special imo, its presentation has been captured in many videos or boomerangs.
and many, many more -- this hardly scratches the surface. sorry I couldn't include photos (there are really too many), but all of these will be easily google-able.