Keep up with the soaked senior feed and alfalfa cubes. Add to each meal 1 cup of flax meal for extra fat calories. To two meals, add a digestive aid like Fastrack or similar.
If she'll eat more feed, and you're at the max recommended senior feed for her target weight, then you can add as much alfalfa cubes as you want. Make a 4th and 5th meal of more of those. Or if you don't want to add more alfalfa, you could try soaked beet pulp shreds with a little alfalfa for flavoring, or Timothy/Alfalfa mixed cubes.
Make sure she's thoroughly dewormed as well.