How is her food intake? Is she eating and drinking? Is she losing weight? Weigh her daily to make sure she is maintaining. If there is weight loss, you may need to syringe-feed her either a critical care food or usual pellets mixed with water and made into a paste. One of the problems with tooth root abscesses is that they are painful and some pigs will stop eating or slow down eating enough that it impacts their health. She is fighting an infection, you don't want her to be deconditioned by lack of food going into this process.
My experience based on dental abscesses with two of my pigs: Make sure your vet has experience with guinea pigs and knows what to prescribe. It's a serious but treatable problem, but an experienced vet and aggressive treatment can mean the difference between a good outcome and a bad outcome. The vet will most likely lance and drain the abscess and prescribe an antibiotic (Zithromax is supposed to be the best, but doesn't seem to be in common use in Canada for pigs. My vet prescribes chloramphenicol, which I've had good results with treating Sundae's abscess. A lot of vets just want to give Baytril, but although it's good for some ailments, it's not that great for abscesses.) The wound will be left open to continue draining. It's not a quick fix and will continue draining pus, so you will need to express the pus that forms and irrigate the wound. This can take a while, because the wound needs to heal from the inside out. It can take months (Sundae had her abscess op in late October and I was still cleaning and irrigating the wound in the spring! At this point, she still has an indentation where the abscess was, but it is no longer draining anything and doesn't need any care, though I still wipe it down and inspect it every few days. Unfortunately, there isn't really a quick fix other than meticulous cleaning/draining while it heals. During that time, make sure the piggy is eating and maintaining weight. It may still be sore to eat, so you may need to supplement until the piggy can eat on her own again.
Hope this helps a bit... it's great you've found the forum here, you will get great info from everyone here!