Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Mia would find a father figure and/or mentor in Ash
The Stinger for the movie is a brief shot of Ash looking at the screen and saying "Groovy". We learn that this movie also takes place in the Evil Dead-verse, so it's likely he and Mia would cross paths at some point. When they both learn that the other has experience with the Deadites, they would sort of bond over that. Eventually, Ash would've become a Parental Substitute for Mia, even deciding to train her in the ways of dealing with Deadites that he knows of. The reason the Spirits in this film are much more serious and no nonsense is due to them NOT being the same spirits as the Original Deadites.
The book can summon other demons, with the Deadites only being the ones to appear due to Ash only really, by accident, forgetfulness or being high, knowing the one spell in the book that specifically summons the Deadites, the spell in this film is a different one that summons a much more serious and to the point evil, kind of like Eligos.