You need to break her bitch shield. Don;t be weak, accomdating, or soft. I don't have experience w brats but maybe:

"Don't be silly. You know what I mean..." (builds intrigue, but don't give her too much)

Or maybe fuck w her and fully own it lmao: "Yes, you're fierce like a lion. I'd be happy to spank that firencess right out of you" (assuming she might be into that, which most brats are I believe)

She seems like a brat type. Where's the soft close exactly? She's been giving you lotta shit ("Bold of you to assume I was going to say yes anyway x")