We had similar concerns about the blood products our child needed during chemo, as well as pre and post BMT. Some blood products are irradiated in addition to being pretreated chemically in order to kill any potential viruses, bacteria, etc. Not sure whether it's possible to do this all the time, i.e. whole blood. Mostly blood agencies rely on the donor's word and some standard lab tests.
I realize that this is no comfort to you or your family. Hope your mother recovers quickly.