What are you opening her mouth for?

It might freak her out, which might cause a defensive reaction (I hate it when the dentist pokes and prods at my mouth, too!)... but after it's over and done with and she's had time to de-stress, I don't imagine that she would be any more aggressive than normal.

You kind of have to hold the snake's head between your thumb and pointer just behind where the jaw hinges, so kind of on the side of where those two visible lumps of the skull are, if that makes sense. . Then use a small, sturdy sterile object to open the mouth.