Any ideas for things for my mom to eat who is on a puréed diet at her nursing home?

To be honest, I would bring her a milkshake; it tastes great, has calories, and will likely make her very happy to get to have such a treat. It's very tough for her to be in such a position in the first place, so my heart goes out to both of you. You are a great daughter (?) to be helping mom like this.

Best of luck!

My husband after almost dying from aspiration pneumonia in 2018 came home on a pureed diet and since I don't really cook all that much, I just pureed everything he normally like to eat, from meatloaf, turkey and gravy, beef stew to different vegetables. I also made his favorite mashed potatoes which were very easy for him to eat. And of course any creamed soups or otherwise as well. And for breakfast you can make either oatmeal, cream of wheat or grits if she's open to that.
It's really not that difficult to come up with things because again, pretty much everything can be pureed.

I had surgery on my jaw when I was a teenager and had my mouth wired shut for 2 months. I can attest to how many foods taste like poop when they are pureed!

The things I enjoyed most through a straw were mashed potatoes watered down with gravy, milkshakes, carnation instant breakfast drinks (chocolate & strawberry), applesauce, and baby food fruits. But the mashed potatoes and gravy were my absolute favorite. I felt full and satisfied, it was almost like having a real meal.

During my mother’s time with puréed foods the thing she liked most was a Wendy’s frosty

There was (almost) nothing that my mom's nursing home didn't puree, I remember tasting her chicken caesar salad (pureed chicken over pureed and thickened lettuce with dressing) and thinking it was really weird and not really worth the effort, but nonetheless it did taste like a chicken caesar salad. Have you spoken to the dietitian or food service supervisor about your concerns?

For those resistant to the idea of pureed foods I think it goes better if you try to concentrate on foods that are normally almost that texture -
mashed potatoes with gravy (some meat can be pureed with the gravy)
as you've mentioned almost any soup is good pureed (thickened if necessary)
lentil dahl
hummus
silken tofu
polenta with marinara sauce, or refried beans
squash and rutabaga are both often served mashed, as are sweet potatoes
grits
guacamole
custards, both sweet and savoury
egg salad
for breakfast cream of wheat or oatmeal with lots of sugar and butter/cream
yogurt, especially greek yogurt
fruit sauces - there's more than applesauce
....

When my dad was near the end egg custard was his favorite. Easy to make slides right down, has protein, and tastes good.

Bone broth spiced up with the flavors she likes will provide protein. It sounds like you've done a great job getting her sweet treats: they all sound good. I love smoothies because you can put so many needed ingredients in it.

When I was hospitalized I found out that some of my medications changed my taste buds.

It sounds like she prefers sweet tasting things. You could also try ice cream and puddings, flavored yogurts, scrambled eggs.

I make smoothies with fresh blueberries, some other berries as well, like raspberries, strawberries will do, all fresh no frozen, add melon any type, pineapple, the banana for thickness and avocado for good fats, you can add some honey.

We used to make milkshakes and fortify them with peanut butter powder, he really liked those and it’s high protein.. Adding Hershey syrup is also high calorie. His doctor said once they get to that stage that any calorie is a good calorie, so don’t worry about a balanced diet. Feed her high calorie foods all the time.