I think you are still confused. Ygritte never claimed the wights are due to opening the graves. The Wildling were already fighting the Others, and losing, and facing larger wight-ified forces next time as a result, before opening the graves. That was when they started burning the dead. The opening the graves to find the horn was to try and bluff the NW into letting them south (from Mance's own mouth) though I think common wildlings like Ygritte thought it was to blow the wall down and escape south.
Opening the graves released shades, according to Ygritte, but this is almost certainly just a superstition. Shades are not wights and no efforts to combat them or physical 'results' are mentioned by Ygritte or anyone else. This is also similar to the Stark (shared gods, First Man heritage and probably other culture) belief that the crypts under Winterfell prevent the spirits (shades) of the dead from disturbing the living. Fairly standard anti-graverobbing cultural beliefs.