The rule of thumb we learn in school is too simple for a case like this.  When we are talking about just red blood cells, O neg is the universal donor and AB pos is the universal recipient.  People who are Rh negative can only receive Rh negative blood cells.  When it comes to plasma, AB is the universal donor and O is the universal recipient, as AB plasma does not have circulating anti-A or anti-B antibodies.  In a sensitive case like this one, an exact match is always preferable due to the health risks of any immune reaction.  Further complicating things, there are several other antigens that may need to be tested for, depending on the nature of the transfusion.

I would, again, encourage everyone, regardless of blood type to donate as often as possible.

Fortunately, it appears that enough donors have been identified.