Yes, she is probably embarrased, and ashamed -- and all of that is perfectly normal for her. Don't push her into accepting him YET. The more you push, the more likely she will resist- and that could last forever. Children have a great need to be accepted socially - having a handicapped sibling is often a HUGE deal for kids- it makes them feel different and fear they will be judged as people judge him.
It is often a lifelong issue for parents who push sibling to love and accept the handicapped child, but is always a huge mistake. Kids don't have the same cognitions adults do, and although we can require it - it won't be genuine. If you want her to genuinely love and accept him - let her come around on her own terms.
In that light - give her another 4-5 years. If not pushed, she will come around to love and fully accept him - and even involve herself in his life.
I hope this helps!