Is it possible that DIL is a direct speaker and you're an indirect speaker? Because her questions seem okay to me.
Q: "Why are the eggs still out"
A: Oh, I got distracted after breakfast.
or
A: They've only been out for 10 minutes or so, I was going to put them away after breakfast.
or
A: Yeah, we kind of got carried away after making the muffins, here, let me put them away.
Q: "why did you dress gs that way"
A: I thought it was cute!
or
A: We weren't going out anywhere today, so I figured I'd let him be comfy. I was going to dress him better (warmly, whatever) if we decided to go out.
Q: "why did you wash that load with the wrong soap"
A: I just used the one on the shelf.
or
A: Which soap do you prefer?
(Or better yet, why are you doing laundry at DIL's? - You should probably stop that. My Mom does some laundry for us but I wouldn't want my MIL to.)
As for the questions to your son:
"why are you so late from work?"
Maybe, he was supposed to be home early, because HIS parents were visiting. Again, I wouldn't want my IL's visiting while my DH went to work. We just don't have that kind of relationship.
"why are you going on that trip for work?"
Maybe she wants to know? I don't get why this is a mean question. Maybe her tone was mean? But maybe she doesn't like when he goes on trips for work and then she's in charge of the kids and the dog without a break. Without even a warm body in the house, so she can go grocery shopping alone. Maybe she can't sleep when he's not there.
"why didn't you feed the dog?"
Was the dog his idea? Maybe they have a deal where HE feeds the dog. I know it sounds petty, but that's how it works in our house too. Sure, I COULD clean the litter boxes and I COULD take out the trash and I COULD empty and re-load the dishwasher, but those are my DH's ONLY jobs around the house. Because honestly, he COULD make the lunches, he COULD get DD's breakfast, or help her pick clothes, or brush her hair, or help her get her stuff ready for school (and that's just the AM routine).
The thing is, especially with the questions to your DS. You're not party to their marriage, you don't know the deals they've made and you don't know how they work things out. ANd honestly, it's none of your business anyway.
I can't remember where I saw this, but it was "lying liars lie" and you know what? Bossy people are bossy. And bossy people think they know what's best.
Unfortunately, as the Mom of her family, she does get to be the boss of things in her house. So the way for you to avoid being bossed is not to put yourself in a position of being "the employee" with her as "the boss". So stop working for her. You get to be the fun Gma who plays with the kids. YIPPEE!
Now, if she starts being bossy to you for other things, you can always answer with humour: "you're not my real mom!" or "you're not the boss of me!" If you say it funny, what can she say?