Snake mites can ride home on you if you go to a petshop and get one on your clothes. And the snake enclosure is their favorite spot as they need humid, warm, dark conditions to thrive and lay eggs. Like i said, check her by running her through a wet paper towel and also check the water bowl for little black specks of pepper.
And she probably didnt get them all of a sudden. Also in my snake room, all i have are 9 snakes and a beardie and i still managed to get mites. Like i said, only thing i can think of is i picked up a hitchhiker on my pant leg or something. Thats why i dont go to shows. If you do though, you should strip in the garage when you get home and throw everything in the washer and then go hop in the shower to prevent bringing anything unwanted home.