Gretel is told by her parents that she has to do the dishes and that she cannot delay or avoid it any further, which is further affirmed by her getting grounded as she forgets to do it anyway. From here, we can establish that Gretel really hates doing the dishes and has frequently attempted to get away with not doing them, which was actually hinted at before. In "Superhero Sibling Rivalry", Kevin argues with Gretel that she has to do the dishes today, to which Gretel objects by saying she did it yesterday. Kevin then states that Gretel's letting the dog lick the scraps off the plates doesn't count as doing the dishes.
Some of the more horrifying things dealt by some of the villains to Gretel get worse tenfold when you realize that Gretel is still a child. This is especially the case with the more psychological damages, such as scanning her subconscious to scare the bejeezus out of her or gaslighting the entire city that she and Hamster are villains that deserve to be arrested. And these (often adult) villains don't seem to care at all that they're giving these mental scars to a 9-year-old. Gretel may not suffer many physical wounds thanks to those superpowers, but that doesn't mean she's impervious to traumatic experiences.
Imagine going on with your day, probably doing some grocery shopping or heading to the gym, when suddenly a U.F.O. shows up, bestows you with superpowers, and the alien inside tells you to drop everything you were about to do and use your superpowers for evil. Do you have any say in this, or are you forced to obey them? The way to make yourself free will feel like an illusion...
In "Romancing the Scone", the U.F.O. is apparently able to blast a target of their desire with "evil powers". It's clearly different from their regular beam, as what the aliens have hit by accident, a scone, doesn't seem to become alive (much unlike the bouncy castle in "Birthday Besties"). This means that the aliens are capable of forcing you to become evil anyway, even after refusing their command.
Isn't it a bit weird that Dave or Carolina don't seem to be aware, or at least don't seem to acknowledge, that there's a duo of superheroes in the city that look an awful lot like their daughter and pet hamster, when literally the whole town is seemingly plastered with imagery of said superheroes and everyone else knows them? There's Hamster and Gretel movies, popsicles, T-shirts, board games, a fan club with tons of members, hell, a live Q&A session only minutes after Hamster and Gretel enter the scene for the very first time... and neither parent seems to know anything about it?! Or, if they do, they never brought it up at the dinner table? Especially considering how the superheroes share the appearances and names of their own Gretel and Hamster?!
They've got to be aware that there's at least a couple supervillains terrorizing their city, right? I mean, they were right there when Carolina's sister Melissa went against El Luchador (a public, luchador-themed supervillain and literal convict who escaped from prison) in a wrestling match!
Speaking of supervillains, where the heck are they coming from? Some people, like La Cebolla, were given superpowers by the aliens just like Hamster and Gretel, and thus would be just someone for the superduo to fight against, but what about those like Professor Exclamation, who decided to become a supervillain before Hamster and Gretel showed up? Was the city already being terrorized on a daily basis by them, or were they only motivated after Hamster and Gretel became a thing?
Two things to consider: one, this series takes place in the same universe as Phineas and Ferb, and two Phineas and Ferb not only had a SuperheroEpisode, but also a crossover with the Marvel Superheroes. The latter can explain why there are supervillains besides the ones created by the aliens. As for why they didn't start supervillaining until Hamster and Gretel arrived on the scene:
Khaka Peü Peü: There's no point in being a supervillain if there's no superhero to fight with.
Season 1
The Bantam of the Elementary School Light Opera
The school has suffered from the curse of the Bantam since the mid-90s, starting with the disappearance of Christine DePoulet. Later in the episode, Hamster and Gretel discover that Christine DePoulet herself has been sabotaging the plays as the Bantam for the past 25 years, never leaving the school theater and having made a living under the stage. But how did she manage to nourish herself for so long without ever being seen? Did she happen to stock a lifelong supply of canned beans? Did she install a minifridge somewhere?
