Sounds like a dominance thing.... but it's probably linked to how much attention she's getting......
Is she still getting regular walks?
From what you've said, this isn't in the night, it's during the day when you are with her (so she could ask to be let out, right?)
I'm no expert, but I find what works best with my dog is actually not speaking to him, when he's been naughty (but, I should add, I've never had a problem with his toilet habits IYSWIM). If he's naughty, I don't speak to him for 5 or 10 minutes. No eye contact, no verbal commands... If we're out, he's put onto a short lead and made to walk by my side (he's usually on a longer lead or carrying his own lead). At home, he'll be made sit on his bed...
After a few minutes, I will talk to him sternly about what the problem was, then put a much happier voice on, bend down on his level and say 'OK, you are forgiven now' (at which point he'll be beside himself with delight and we'll have a cuddle and maybe a little treat)
Anyway, I think the first step is to look at whether she needs more exercise / time outdoors. I would like to add, IMHO, an 8 month old puppy should not be toileting indoors at all. It sends a confusing message.
Good luck.