Well, I can think of two things that might be the problem:
-Almost all the foods you listed are either processed with some salt or some sugar, so she'd naturally have some taste preference for them.
-Mashed potatoes, among other foods, have a distinct texture that VERY many kids are bothered by. My oldest has issues with some foods over testure as well, potatoes being near the top of her list too - she's not even really into french fries (which is fine with me, because as "food" they're AWFUL! LOL). And frankly, potatoes have a pretty high glycemic index anyway (meaning they convert to sugar fairly quickly in the digestive process), so there are plenty of other foods that are better choices, like ANY green veggies, for example.
For stew, I'd just stick with veggies you know she can handle, and not even blend them, just cook them soft and, well, stew-y, and let her at them - carrots, green beans, peas, maybe corn, maybe lima beans (Josie is the ONLY one in our house who'll eat them LOL), some onion chunks, perhaps even some broccoli florets. The starchiness of the potatoes feels kind of grainy in the mouth.
If it's really important to you that she eat potatoes, try slipping a MINISCULE (i.e. UN-noticeable) amount into the food for a few days, and then EXTREMELY gradually increase the amount. If it still bothers her in such small quantites, I wouldn't push it. There are lots of kids for whom the texture of food can make or break a meal, who are over-sensitive to certain sensory stimuli (as Josie and I are), food texture being one of many issues they have, so it might no tbe picky, it might just be an issue with the feel of it and/or the taste of it in her mouth.