That is true. But if taking proper thawing procedures the rat isn't going to bite your snake if you leave it in with them.
I don't believe any one has encountered any problems directly from unsafe amounts of bacteria but I personally would not take out a rat and thaw them in hot water or leave them on the counter. You are creating an environment for parasites doing that. I put food in the fridge to thaw before I leave for work in the morning and feed late at night when I get home.
Yes snakes eat tons of parasites and whatever else in the wild but these are captive bred animals who didn't ask us to cage them up. The least we can do is provide them a clean house and good food.
Op you can feed once a week if she looks skinny or you can feed every 10. She will be fine either way
If her house has hides and water I would allow her time to settle