He's already really close and getting closer. She cocks her head to the side in curiosity and confusion before her eyes go wide in understanding.

"Oh...uh..."

The blush she'd been cultivating deepened to a beet red and her heart starts to flutter. She's surprised at his boldness. She's even more surprised at herself. Those are definitely butterflies in her stomach.

...She can fearlessly face down hordes of zombies but the prospect of a kiss gets her tied up in knots?

It's not even that she doesn't want to, but she has no idea how to proceed. How do you do a "real kiss?" What does that mean? Where do you start and where do you go?

Unbidden by anything but Dipper's use of the word 'great', her father's advice comes to her head. 'If you get too worried about what could go wrong, you might miss a chance to do something great.' Even though this is...probably not what he meant. And she's going to go ahead and feel confident that he'll absolutely like and approve of Dipper.

She's starting to feel like she's stalling and he deserves an answer. An answer that she doesn't seem to be able to find the words for. Another thought jumped into her head:

'If you're going to do it, just do it.'

She closes the distance between them and plants her lips on his.