What's the meaning of independent "as if"?

as if
—used to say that something is not true, not possible, will not happen, etc.
// "I am sure I am very affectionate," said Dora; "you oughtn't to be cruel to me, Doady!" "Cruel, my precious love! As if I would—or could—be cruel to you, for the world!"
— Charles Dickens

—sometimes used informally as an interjection to say that something suggested or claimed is impossible, incorrect, or ridiculously unlikely to be true

// A simple collection of songs? As if. How about a conceptual ode to London's millennia-old history? — Craig McLean

// Big budgets? High-priced actresses? As if! The film cost a modest $13 million, a figure achieved by not casting stars, but rather stars-in-the-making …
— Nicholas Fonseca

Rachel says "as if" to reject the compliment.

As a aid, you could conceivably think of this as as if that were true/as if I were foxy/as if I were a foxy lady. But it is unnecessary. She's simply expressing that she does not believe she is foxy.

→ Yeah, right. As if that were true.
→ Yeah, right. I am not a foxy lady.