I'm a SAHM.
But that does not matter.
When kids are irked, they say things like that sometimes.
My kids included.
Once, my son had a minor cut on his thumb. He was being all drama. I put a Band-aid on after putting Bactine on it, then went about my chores. He then, CRIED and said to me all exasperated "MOMMY I thought you were going to take care of me! You're not doing that!"
Ugh.
However, your 7 year old is old enough, for you to talk to her.
My daughter has asked me, "Mommy how come you don't work like the other Mommies and make money?"
She was about 5 when she said this.
I then... per her cues, FULLY explained that all Mommies are Mommies, but we each do different things. Some work. Some stay home with their kids. But we all do what we have to or can. I explained that me & Daddy decided that I would stay home to be with her/brother and raise them. That all Mommies, take care of their kids and families, differently etc.
Then, sometimes my Daughter will say that when she grows up she wants to be a SAHM just like me. Of course whoever is in earshot and hears this, all gasp and tell her "You can be anything you want! You can be something important like a President! not just a Mommy" (as though a SAHM is, nothing 'important.').
So, it goes both ways.