After discussing this with several gringas also dating Brazilians, I feel better knowing I am not alone.
Eli's mom enjoys coming over to our apartment to clean and cook, sometimes with an intentional plan and other times making an executive decision to do so upon arrival. Even though she doesn't in any way intend to offend me, it always seems they don't think we're doing a good enough job taking care of ourselves and that the troops must be called in to get the real job done...which in the end does bother me.
This weekend, there was a definite plan, one that was not asked or requested, but rather informed. I'm coming over to clean. Period. When I woke up on Saturday morning, she was vacuuming the living room, with Eli's sister on the couch reading, while Eli's dad played computer games until lunch. She also brought a window vapor cleaner thing and used up half of our cleaning supplies--even though we'd already cleaned most of the apartment a few days earlier. Eli and I helped, though I spent half the time running around putting stuff back into place that had been rearranged (I'm OCD like that).
That day was an exception to the rule, since we went out for lunch, but usually on days like that Eli's mom brings ingredients and makes rice, beans, some sort of meat, and juice and then leaves the leftovers in our fridge. She never seems to think either of us eat enough, and she sometimes seems offended if I don't take more than two servings. This part I mind less.
I've heard from others that this is not uncommon for family members (always women) to come over to clean and cook, whether it's just because or for an event. Family ties in Brazil are much different than in the States, and this includes taking certain liberties with relatives. In the US, going over to someone's house to clean without asking permission first is moderately offensive in the least, and I've learned the best way to deal with it is to bite my tongue and stay out of the way.