A woman does not have to sit when doing ghusl
Question

                Does a woman have to sit while taking a shower or it does not matter?
Praise be to Allah.It is not obligatory for a 
    woman to sit when doing ghusl, rather she may do ghusl however she wishes, 
    standing, sitting or lying down. The same applies to men. 
There is also nothing wrong 
    with a person doing ghusl naked, as is explained in the answer to question 
    no. 6894 and
    6976. 
Some fuqaha’ regarded it as 
    mustahabb for a person not to stand when naked, when doing ghusl and 
    otherwise; rather he should crouch so as to cover himself. 
Ibn ‘Abd al-Barr (may 
    Allaah have mercy on him) said: A man should not stand up straight when 
    naked by night or by day. When he does ghusl he should crouch as much as 
    possible, for Allaah is more deserving that he should feel shy before Him. 
    End quote from Haashiyat al-‘Adawi ‘ala Sharh al-Risaalah (2/455). 
This has to do with modesty 
    and covering, but it is not obligatory. 
And Allaah knows best.