Continuity mistake: Linda's head in the vise changes from at an angle in shots from behind to straight up in front shots. (00:20:30)
Continuity mistake: Linda's hair is dark as it rolls toward her standing headless corpse, but blonde as it attaches. It's dark again as she bangs Ash's head against the window blockade, but blonde when her head falls off a moment later. (00:17:50 - 00:18:45)
Continuity mistake: When Ash leaves the workshed after cutting up Linda he only locks the door to the workshed with the chain, later on he goes into it and unlocks the chain and the piece of wood. (00:22:20 - 01:06:20)
Continuity mistake: In one scene, Ash finds some pages from the Necronomicon lying in a mud puddle. He picks up the pages, and they're dry. (01:10:00)
Answer: Sam Rami could not get the footage of Evil Dead to use in the sequel, so he remade the movie in a shortened form for the beginning. Since Linda was the only original character other than Ash to come back he included her in the recap but deleted the others as not to waste time. An in universe answer could be that trauma of losing his friends made Ash block them out and rewrite history in his head, except for Linda who comes back to haunt him in the movie so he is forced to deal with it.