She is taking care of her disabled brother and her parents want her to get married

You have done a good thing by taking care
of your brother; this is an act of kindness towards him and towards
your parents.  But marriage is a Sunnah, one of the ways of the
Prophets, which Allaah has prescribed for His slaves and He has created
them with an inclination towards it. I think that you have the choice
of a number of solutions, as follows:

If you can afford to hire
someone to take care of your brother, this would be good. Or you could
look for some good people who would sponsor all or part of his care.

Or you could get married and have your
brother come and live with you, so that you can carry on looking after
him.

If you find someone who agrees to get
married on condition that you stay with your parents in order to take
care of your brother, and your husband comes to visit you in your house
or you go out to visit him sometimes, this may be a good idea.

If none of these solutions
are easy for you, and you feel that delaying marriage will not cause
fitnah (temptation) for you, there is no sin on you in that case. But
if you fear that you will be subjected to fitnah, then it is better
for you to get married, because this will protect your religious commitment,
and serving your brother is not an obligation upon you, rather it is
voluntary good work.