In Ethan Frome, based on Chapters 1-5, why is Zeena dissatisfied with Mattie?

Mattie is not a very good housekeeper, but she tries hard
to please Zeena--an impossible task. Zeena is so cold, critical, and self-centered that
no one would be able to please her. Zeena's dissatisfaction with Mattie, however, grows
as Zeena becomes aware of Ethan's interest in Mattie. Zeena watches everything and
little escapes her notice. She observes, for instance, that since Mattie's arrival Ethan
has begun to shave every day. It is also significant that the night Ethan walks Mattie
home from the dance, Zeena has locked them out, making sure she knows when they come
home. She is suspicious of their relationship and threatened by Mattie's presence in her
house. Zeena responds to Mattie's youth, beauty, and goodness by voicing continual
criticism of her and by treating her in a cruel manner.