Hello! I am a registered dietitian who has clinical experience both in a hospital and long-term care facility. I also have a 94 year old grandmother who barely eats these days, so I can relate to seeking out high protein foods.
First, did your mother receive a swallow evaluation at all while in the hospital? Usually elderly patients who suffer from a TIA may have some residual effects such as poor swallowing. If you think her swallowing is fine and she is not at risk of aspriation, then I would experiment with different types of high protein foods and supplements.
Have you tried any of the high protein liquid supplements, such as Ensure, Ensure Plus, or Boost? That would be my first try because they are very high in protein, vitamins, minerals, and come in sweet-tasting flavors such as chocolate, vanilla and strawberry. There is a protein "shot" that we used in the hospital called ProSource. It is not sweet-tasting, but you can add it to sweet foods like pudding, yogurt or applesauce. Ensure also makes puddings, though not as high in protein as the bottled shakes.
As for "real" foods that are somewhat high in protein (although not as much as the supplements) and sweet-tasting: flavored yogurts, peanut butter, chocolate milk, puddings, Carnation Intant breakfast. You could make your own shake with milk, ice cream, and berries. The milk will provide a good dose of protein. Also, Silk Vanilla soy milk is pretty yummy and a good source of protein.
High protein plus sweet tasting can be hard to find. You could make French toast and drizzle with syrup. Other sources of protein (minus the ones you said she's not liking), but not sweet, include: eggs, cottage cheese, regular cheeses, nuts (although I'd be careful with these based on her chewing/swallowing ability.
If you can get her to drink the supplements once or twice a day, and switch it up with one of the other suggestions, that my keep her from getting bored. Good luck!