First, is it an actual COOKING cup or is it just "oh, i found this plastic container i'll say it's a cup" cup? Because that's what my friend did with her dog, and the container actually had about 3 cups in it.

And if it is an actual cup...

Rien eats HIGH QUALITY food and he gets 3.5 cups a day.
He's about Roxy's size, but obviously he gets more exercise, being that he's not on a chain 24/7 (minus maybe an hour). With CRAP food, I'd go with at least 4-5 cups a day. No wonder she's so thin. She's STARVING.