Ok , so 3.8 lbs is 1724 grams. She is a pretty healthy senior citizen, haha. I would cut back her meals to once every two weeks. And it is better to give one appropriate sized meal. Even if you go up to medium rats for her ( at that weight) is fine. Also make sure the meal is leaving a slight bulge in her but isn't very much wider than her girth at the widest point of her body. Good luck and don't over feed her.