If The Hemoglobin Is 7.4 Can It Be In Normal

If the hemoglobin is 7.4 can it be in normal range in 2 days? My mother in law had hip surgery 2 days ago . Her hemoglobin was 7.4 she is severely malnourished due to hx of gastric bypass surgery. Weighing only 98 lbs. I was told by her daughter the dr said her hemoglobin is now 12.0.. That to me is hard to believe.. No blood was given , no iron, nothing.