Yes. Kristen Stewart wore a wig as Bella Swan in Eclipse. The reason fans usually cite is that she had cut and dyed her hair for The Runaways, so Bella's long brunette continuity needed help.
Why people noticed
The wig sits differently from Stewart's natural hair in the earlier films. The density, shine, and hairline sometimes look less effortless, especially once you know to look for it.
Why the production used it anyway
Movies need character continuity. Bella could not suddenly appear with Joan Jett hair because the actor had another role.
Bottom line
Kristen Stewart did wear a wig in Eclipse. It solved a continuity problem, even if fans still debate how convincing it looked.