Islam strongly stands for respect and love among couples and their in-laws, be it mother or father, son or daughter. Thus, mutual love and compassion among in-laws are among the main purposes of marriage.
It should be clear that there is no compulsion upon a daughter-in-law to serve her mother-in-law or father-in-law, but there is a duty upon her to respect and love them and if she has served them out of respect and kindness towards them, she will be greatly rewarded by Allah for that.
The Muslim wife who is really committed to her religion should look at them as her own mother and father. They also have to consider her as their daughter. They should not treat her as their slave or servant. Islam calls for piety, love, mercy, compassion, and cooperation. No one should use others as servants, but as human beings and fellow Muslims. This also goes for the husband at the same time.