All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is not permissible for a wife to refuse to go to bed with her husband [for sexual intercourse] on the grounds that Ghusl (ritual bath) harms her hair or her health as the Prophet said: "If a husband calls his wife to bed and she refuses, the angels will curse her until she gets up in the morning." [Al-Bukhari and Muslim]
However, if she has a sound reason for fearing about her health, like when it is cold and there is nothing to warm the water with, for example, then she may perform Tayammum (dry ablution) instead of Ghusl and then she performs Ghusl when her excuse disappears.
Therefore, a wife should obey her husband when he calls her to bed and it is not permissible for her to refuse unless she has a sound reason like menses, or an obligatory fasting and so forth. Just fearing to perform Ghusl is not a sound reason for refusing.
Allaah Knows best.