She respects her mother-in-law more than she respects her mother!

Allaah has prescribed the best and most just of rulings,
which bring happiness to individuals, families and societies. Hence He has
prescribed rights and duties for every individual in society, so life will
run smoothly and each person will know what he is entitled to and what he
must do. 

The husband’s rights over his wife are great, and have to do
with him, his wealth, his house and his family. Showing respect to the
husband’s family, especially his parents, is part of showing respect to
one’s husband and treating him well. When a woman does her duties towards
her husband, she is obeying her Lord and has the hope of reward from Him.  

Honouring your mother-in-law is something that is to be
appreciated, and no one can deny that. Rather what you are doing is in
accordance with Islam and common sense. By doing that you are earning the
pleasure of your husband and contributing to the success of your marriage
and protecting it against things that may spoil it.   

But one should not obey one’s Lord in one way and forget
other aspects. It is not permissible for your respect towards your
mother-in-law to be at the expense of respect for your own mother, because
parents – and especially the mother – have important rights over their
children. See the answer to question no.
5053 for more information on the
mother’s rights over her children. 

You have to honour your mother and treat her kindly even if
she is a kaafir, as much as you can and as much as your circumstances allow.
But if she calls you to kufr and strives to make you follow that, as our
Lord says (interpretation of the meaning):  

“And We have enjoined on man to be good and dutiful to his
parents; but if they strive to make you join with Me (in worship) anything
(as a partner) of which you have no knowledge, then obey them not”

[al-‘Ankaboot 29:8]

and  

“But if they (both) strive with you to make you join in
worship with Me others that of which you have no knowledge, then obey them
not; but behave with them in the world kindly”

[Luqmaan 31:15].  

So what are her rights over you if she is a Muslim who
believes in the Oneness of Allaah (Tawheed)? 

It was narrated that Asma’ bint ‘Abi Bakr (may Allaah be
pleased with her) said: My mother came to visit me when she was a mushrikah,
at the time of the Messenger of Allaah (peace and blessings of Allaah
be upon him). I consulted the Messenger of Allaah (peace and blessings
of Allaah be upon him) and said: She is expecting (something), should I
uphold the ties of kinship with my mother? He said: “Yes, uphold the ties of
kinship with your mother.”  

Narrated by al-Bukhaari (2477) and Muslim (1003). 

What is meant by expecting something is that she wants her
daughter to honour her. 

So do two good things at the same time: honour your mother
and your mother-in-law. If there is a conflict between the two, then do not
give your mother-in-law or any other woman precedence over your mother, so
long as that will not cause any trouble between you and your husband. 

We ask Allaah to help you to do that which pleases Him and to
make you among the woman who are righteous and devout. 

See also the answer to question no.
22782 and
5326. 

And Allaah knows best.