Well for one thing, trying to feed her every few days is too often. She should be fed once every 7 days up until a year old, then feed every 10-14 days. She should be fed prey items the same thickness as the widest part of her body. How long is she? Newborn boas or boas a few months old can start eating rat pinkies or rat fuzzies... you can feed them mice, but rats have more meat to them and are healthier.
As for the
mites... they are little black specks in her scales, right?
You can go to your local walmart and in the camping section you should find an orange and blue metallic can of Repel Permanone with .05% permethrine in it. NO DEET. Taking her to the vet will only stress her out right now and isn't necessary yet.
If you're using aspen bedding, cypress mulch, or even newspaper.. if you're using newspaper, shred it up finely, preferably with a paper shredder and use that for substrate.
Take the snake and waterbowl out of the enclosure and temporarily have the snake in a small container. With the Repel, spray down the enclosure and bedding really good, stirring the substrate and spraying some more. DO NOT put the snake or waterbowl back in yet. Close up the enclosure and let it sit for about 30-60 minutes, then let it air out and dry completely for 60-120 minutes. Then put your snake and waterbowl back in. The reason for needing loose substrate for this is so the snake's body can come in contact with the Repel and it will be of better use to kill the
mites.
Repeat this in 2 weeks. This is so that any remaining
mite eggs that may have hatched will die also.
Also, do you have any other snakes? And if you do, are you quarantining her in another room? It is important that you do that for 6 months... if her enclosure was near any other snake enclosures, you're going to have to treat those cages too and spray the Repel around the outside of the cages lightly. If she is your only snake, then you should be fine.