He stipulated that she should look after his father, then he took a second wife and she asked him for separate accommodation and to divide the work with her co-wife
Question

                The questioner got married to a woman after explaining to her his father's situation, as his father is sick and needs someone to take care of him. She agreed to that, but now he wants to marry a second wife, but the first wife said: If you take a second wife, then it is my right to ask for separate accommodation and to share the care of your father between us (wives). What is your opinion on that? The questioner is saying: How can she request this when it was stipulated from the beginning that she should take care of his father; in fact he only married her for this purpose and no other?.
Praise be to Allah.Allah has 
    enjoined fulfilment of covenants and promises. He says (interpretation of 
    the meaning): “O you who believe! Fulfil (your) obligations” [al-Maa’idah 
    5:1]. The most important covenant that is to be fulfilled is the 
    marriage contract, whether by the husband or by the wife. It was narrated 
    that ‘Uqbah ibn ‘Aamir (may Allah be pleased with him) said: The Messenger 
    of Allah (blessings and peace of Allah be upon him) said: “The condition 
    which most deserves to be fulfilled is that by means of which intimacy 
    becomes permissible for you.” Narrated by al-Bukhaari (2572) and Muslim 
    (1418). 
Based on 
    that, what is required from the wife is to fulfil the condition that her 
    husband stipulated, which is to serve and take care of his father. It seems 
    to us that the wife has no right to ask him to divide this work between her 
    and her co-wife, because that was not stipulated in the marriage contract; 
    furthermore, she knows that Allah has permitted him to marry another woman, 
    and she did not stipulate that he should not take another wife. 
As for her 
    request for separate accommodation, she has the right to that unless it was 
    stipulated before marriage that she should take care of his father in his 
    house and that she would not have accommodation separate from his father. In 
    that case, she is obliged to adhere to the two conditions regarding 
    accommodation and taking care of the father, and she does not have the right 
    to ask for separate accommodation or for the work to be divided between her 
    and her co-wife, unless the husband doest hat on his own initiative. 
If the wife 
    cannot put up with her new situation, then she has the right to ask for 
    khula’ (a type of divorce), in which she will give up her mahr to her 
    husband and he will divorce her (talaaq). 
For more 
    details on khula’, see the answer to question number
    26247. 
We advise 
    the husband to be wise in his conduct and to fear Allah with regard to his 
    first wife; she has accepted him as a husband and has agreed to serve his 
    sick father. It is not right to respond to that by bringing in a co-wife who 
    will not share the work with her and will have advantages over her which 
    will cause him distress in his life and cause him trouble. 
We are not 
    trying to forbid that which Allah has permitted of plural marriage; but we 
    are aware that part of good attitude on the man’s part is responding in kind 
    to the one who has been kind to him in word and in deed. We do not think 
    that the husband’s insisting on not making his second wife share the work of 
    caring for his father is a good way of responding to his first wife’s good 
    conduct. He should stipulate for the second wife what he stipulated for the 
    first; that is what is fair and wise. 
Whatever the 
    case: 
We think 
    that this wife should adhere to the conditions of marriage that were 
    stipulated for her, but she has the right to ask for khula’ if she fears 
    that she will not be able to fulfil the conditions or fulfil her duties 
    towards her husband. But we think that the husband should do the right thing 
    to get out of this situation, which is stipulating for the second wife what 
    he stipulated for the first of caring for his father. If the marriage 
    contract has been done without that, then he has to deal with her kindly and ask her to serve his father and look after him, working with his first wife. 
And Allah knows best.