Alice Harker is mentioned multiple times in the books through memories of characters or just being mentioned. She takes her daughter, Kate Harker, away to a house far away from verity after things get dangerous. After a little while, Alice takes Kate back to Verity. Kate begs to go back home, and eventually, Alice gives in. Alice takes Kate away, but they never get to the house. Alice dies in a car crash, caused by Sloan.
Kate Harker is the daughter of Alice Harker. Kate loved her other deeply and was very sad when her mother died. Kate ended up blaming herself for the death of her mother, as it was her who begged Alice to take her back home.
Callum Harker was the husband of Alice Harker. It is showed that he used to love Alice very much, but wasn't sad at all when she died since he believed she didn't love him any more and only loved Kate.
From what information is given in the book, it can be presumed that Sloan didn't really like Alice. However, there isn't enough information given to say much more.