I recall, omnivores that they are, they ate just about everything they were given. That is not always a good thing.

Your Mom has an important point, that Turtles should not live by floating turtle sticks alone. Live foods, for turtles, just as for fish, cause a feeding response. Animals get bored too and it is healthy to vary their diet and experiences.

A quick Googling of turtle foods show me that the hobby has come along way since we tried feeding them those almost always rejected dried flies and greasy hamburger! (That always meant that the water had to be changed shortly thereafter.) People are also learning to keep them in homes more resembling habitats and not little prisons in bowls.

There are lots of alternatives to feeding them your guppies. You and your Mom are probably familiar with the lists below, but I though it was interesting what was useful and what was not.

Some things, like chicken and maybe other lean table meats, should always be cooked. (Salmonella is all too common on uncooked chicken. Always wash your hands after preparing it.) They should be cut or shredded to size.

Reptile people (Herptile people actually) are really into making sure their pets get the right vitamins and minerals. Those concerns are just getting into the fish hobby now. (See Dr. Terry Fairfield's comments on disease prevention through a balanced diet and vitamins.)

If any of you have large fish, you may have fed them something like frozen silversides. The turtle people (sounds like the name of a cheap science fiction thriller) have noted that freezing fish destroys some key vitamins (less B1). Duh! I never would have thought of that. Maybe buy a small slice of some white fish at the grocery, just refrigerate and feed your larger fish pieces. One could scrape it with a knife for their live bearers.

Here's some more from my hastily assembled notes:

Among the things correctly offered as food were:

Feeder Items: live feeder fish (guppies, goldfish, minnows), earthworms, crickets, waxworms, earthworms, silkworms, aquatic snails, shrimp, krill, mealworms, aquatic snails/slugs, crickets, all kinds of earthworms, live insects, whole fish and crayfish.

For very small turtles, prey may have to be cut into smaller pieces or fed blood worms, Daphnia, mosquito larvae, Gammarus.

Larger turtles can be offered larger items including pinkie mice and tadpoles. (I wouldn't)

Also one could offer fruit such as figs, grapes, cantaloupe, blackberries
Greens such as turnip greens, romaine and red lettuce (NOT head lettuce), dandelion, chickweed, plantain weed, carrot tops, endive, fig leaves, grape leaves, collard greens, turnip greens, alfalfa, and clover
Vegetables such as squashes, peas in the pod, sweet potatoes, okra, sliced carrots, green beans, wax beans, corn, peas, carrots, tomatoes, berries, apples, melon,
Aquatic plants: water hyacinth, water lilies, Elodea and duck weed, or most any extra aquarium and pond plant.

Okay on occasion-- strawberry, apple, citrus fruits, blue berries, leaf lettuces, bananas, dry cat feed, cuttlebone.

High purine (acidic, nitrogen rich) foods which include peas, beans, mushrooms should be used sparingly because they can contribute to gout if overused.

"Empty" food like lettuce and celery. They provide very little useful nutrition or fiber. Only use it to entertain a turtle that is already well fed.

What you should avoid feeding. Note the conflicts with the above: Other animal protein: cooked chicken, lean beef, beef heart.
Leafy greens: collard, mustard and dandelion greens, kale, bok choy. Head (iceberg) lettuce should never be feed as it contains very little nutrition.

Food high in oxalic acid like spinach, chard and rhubarb. (Oxalic acid blocks the absorption of calcium. These foods cause the turtle to become calcium deficient even if a good source of calcium is provided.) This may also be an issue for guppies.

Also avoid cabbage, brussel sprouts, broccoli, bok-choi, and kohlrabi (brassica family). In excessive amounts of these plants contribute to kidney disease and goiter. Turnips, soybeans, radishes, rapeseed, and mustard also contain goitrogens. These should be used rarely. However, the addition of to the diet may reverse the goitrogenic effect of the brassicas.

Obesity and begging are problems. Sound like our fish.

A good reptile multivitamin with calcium and vitamin D3 should be mixed with the food a couple of times a week. Also, an excellent way to provide additional calcium is by putting a cuttlebone in the turtle tank

Turtles like red-eared sliders can live for 10-12 years. The larger ones should get less protein. Commercial foods should be no more than 1/4 to 1/3 of the total diet, depending upon which authority one listens to. Older ones want, but need less protein.

Animal Protein, depending upon who was read, should constitute no more than 25% to 50% of the total diet) Plant matter could be 50% or more of the total diet. Probably the those percentages could be filled out with commercial turtle foods

It sounds like you can pick and choose according to your sensitivities/convictions and still do very well by what you feed them.

About two years ago a guy visited this site and mentioned that he had been raising and feeding his guppies to his turtle. Wow! Did he get beaten up here, especially by the girls. He had begun to appreciate the guppies as guppies and did begin to investigate other Turtle foods.

I never would get attached to crickets (which we raised and fed to my son's anole). Probably live foods can be found which would not bother you.

If feeder fish (goldfish, rosy reds, bait fish) are purchased for turtles, I would quarantine them and treat them with one of those parasite meds. I don't say that as a herp person, but as a fish head. All parasites will not travel from cold-blooded animal to cold-blooded animal. But some will! Those feeders, confined as they have been, are traveling museums of parasites and more. Why take chances?