Depends on her mood and the type of bad the book is. Sometimes a book can be mesmerizingly bad, so much so that she's entertained by the sheer ridiculousness of it. But if it's bad in a way that just offends or irritates her, it's going straight back down and she's moving on to something that she'll actually enjoy.

That said, even the worst books she usually tries to give a fair shake to. After all, some stories really don't pick up until the first quarter or so is past.