Hi and so sorry that you're friend is in this predicament.
It is only a question that the mother and father can answer. Personally, I feel life can be tough enough for kids who are born with no health issues. For children with difficulties it can be twice as hard, sometimes twice as cruel. But there are always exceptions of course.
But with regards to yourself. You may not be able to answer your friends question, but you might be able to help her come to her own decision. Ask her what she feels her instincts are telling her? Ask her to write down her feelings and thoughts if this helps. But at the end of the day she is the only one who can make the final decision.
For your sake, you need to give the question and the responsiblity back to her - not unkindly. But when she asks, you should gently turn it around and simply say to her 'what do you think?' In this way she is the one who has to make the choice, not someone else. Secondly it puts the burden - horrible as it is - back to the only person who can make a choice. This doesn't mean that you are not supporting her or that you are uncaring. But she has to realise that no one can make this decision for her. They can support her. Help her to work out her feelings. But the end decision has to be hers. Hope this helps and bit and lots of luck to you and your friend.