Is it permissible to marry the daughter of a maternal uncle, given a desire to help her mother with household affairs?

If your female cousin agrees to marry you and serve your mother, there is no harm in that; in fact, it is a good thing that combines many benefits, such as marrying someone you love, honoring your mother, the wife's kindness to her husband, and maintaining kinship ties. However, if the wife does not agree to serve your mother, you cannot force her to do so.