You can go to the vet for mite treatment or if you feel comfortable you can treat her at home. For directions for treating pigs for mites at home can be found here: guinealynx.info/ivermectin.html. All it takes is 3 treatments 7-10 days apart. If you don't feel comfortable treating the pig yourself go to a vet. You can harm the pig if you overdose.

If you do go to a vet just get the mite treatment. They may try to do a skin scrapping but I would advise against that. They are painful and inconclusive. Most of the time even if they don't find mites they'll still treat anyways. Treating a pig without mites won't hurt the pig. It's better to treat the pig as a precautionary measurement because mites are painful and can be deadly left untreated.

You can trim your pigs nail, there really isn't a reason to go to the vet. If you are unable to hold the pig still and safely trim the nails then the vet would be your best bet. You wouldn't want to accidentally trim too much and hurt your pig.

You also consider registering at www.guinealynx.info/forums/ - there are many knowledgeable people on this site. If you need help with anything someone there will definitely be able to assist you. Just a warning, the people on that site are mostly adults and care about animals before people. The users may seem harsh at times but they are your best bet for quality and correct guinea pig advice and information.