However, her blood type is rare (AB−) and although she is high on the transplant list, chances are low she will get one in the next couple of days. Her brother, Sam, offers to donate his own liver, because he is a perfect match.
Despite her rare AB− blood type and being at the top of the transplant list, there's little chance she'll get a new liver within the next few days.  Her brother, Sam, steps forward to offer a donation as a perfect match.