I know obviously chemo can drop your counts, but is she bleeding from anywhere? I would make sure her coags are ok, pt/ptt inr and plts.
Also, you may want to get her iron levels/ferritin drawn. Sometimes chemo can also cause an iron deficiency anemia and she may need to get iron.
Red cell transfusions don't last forever, so I guess it's possible she gets a bump from the transfusion and then goes right back down with more chemo.
I would not worry about getting the blood with the chemo on the same day. the only thing I would be concerned about is the amount of fluid it is. Sometimes they give lasix if they think they are giving too much fluid.