Any ideas for meals that I can prepare in the morning and a frail senior can serve by themselves in the evening?

It might be better to have her eat her " main" hot meal in the middle of the dsy, if that's when someone is there to assist. Perhaps then, she could eat a cold salad and sandwich for dinner. Have you looked into Meals on Wheels?

If she'd like to have a hot meal in the evening, I would suggest something like a thick soup. You could make up large batches and freeze them in small containers. Can she still manage container lids?

Another thought is a small crock pot. You can set it up in the am with meat, vegetables and stock, turn it on and it would be ready at dinner time. Let us know how this works out.

Oh!! Don't forget the cookies!

If you are giving her a hot breakfast and she has access to meals on wheels for a hot lunch, then I think the idea of a lighter supper of soups, sandwiches, muffins, fruit cups etc is probably the better option. Often older people have more trouble with indigestion if they eat a large meal at night, and she doesn't need as many calories a someone who is more active.

When are you there? Over lunch? Make THAT her big meal. For supper, make her meal either cold or room temperature. Dinner plate, or better, a compartmented paper plate, covered with Saran and including utensils, and she's good to go.

Ideas for a light supper might be tuna salad with a thick sliced tomato, crackers. Maybe cottage cheese, sliced fruit, veggie crudités with ranch dip. Ham sandwich with Sunchips and a sliced Apple. You get the idea.

Since the container must fit in the basket on the walker, it would have to be smaller containers like a cup or saucer, since a full plate wouldn't fit. To keep it from spilling, she would have to put the top back on the container when she removes it from microwave to the table. I can't imagine moving hot food that way for someone who has mobility issues. I'd be concerned with it spilling and burning her. So, I agree with those above and would only prepare cold dishes like sandwiches, cold cuts, chicken salad, fruit salad, pasta salad, etc. if she has no assistance to prepare the food. To me, her using the microwave would be too risky.

First, find out what she LIKES to eat, there's no sense preparing healthy meals if she won't eat them. Almost anything can be made ahead and re heated later, all you have to do is glance at the frozen food aisle in the supermarket to see that! Casseroles reheat particularly well, but your basic meat and potato meals can also work if you remember microwave basics and place the meats in the centre of the plate and veggies around the edges.
You say she is frail, not suffering from dementia so I don't think there should be a problem with the microwave. Ensuring that the containers you choose will be deep enough to prevent spills and easy to handle when hot will make transferring them safer. There are also trays designed to fit on some walkers/rollators, that might work better than a basket as it would be higher. Don't forget a separate cup holder!

Thank you all for the input. I just met her on Friday and all we did was talk. She is mentally sharp. I'll ask her to move a container of cold water from the frig to the microwave and microwave to table (still cold) to see how well she can handle it to see if it might be dangerous for her. I'll also have her demonstrate how well (or not) she can open her containers. I had already thought about the cup holder too. I'll be there late morning to cook a hot breakfast. My time there will be approximately the same as the delivery time for the local Meals on Wheels, so that doesn't help. I like the cookie idea and I'll check about a tray instead of a basket for her walker.

Thank you again for all of the comments and suggestions. J

Meals on wheels usually brings two meals, a lunch & dinner. In assisted living, lunch is the bigger meal, dinner is fairly light and includes a single serve cup of applesauce or Jell-O/pudding that they can keep in a small fridge in their room. They also serve a small evening snack, such as a cookie or apple or ice cream cup. You could cut up some fresh apple and toss it in orange juice to keep it from getting brown, then put it in a small Ziploc in the fridge for later.

I make baked turkey or chicken wings in ziplocs, sliced baked sweet potatoes, egg salad, sliced fruit and store bought cole slaw, hummus, olive bread, tuna salad, rotisserie chicken. Mom enjoys.

As well as a tray on walker for carrying small things think about a small bag fixed with carabiner clips (when I visited NY I found them in Home Depot).
For light treats jello with small pieces of fruit in it. I don't know if you know Thermos Flasks (I'm in UK), these are good for soups, casserole with small pieces, drinks. Sandwiches cut into shapes with cookie cutters make for fun if finicky eaters. Cutting fruit/veg into shapes helps too. Pasta shapes