Doctors told my girl friend that her body can't produce enough bone marrow, what can she do? is it serious?which foods are useful for this condition?

Could be serious: She needs to be under the care of a hematologist, a specialist in blood disorders. As long as she is making adequate amount of blood(can be checked with a cbc, blood test), she is not in any immediate danger. But sometimes bone marrow can shut down production completely. This may be a serious problem... Should seek second opinion, if need.