Abscesses can puff up very quickly (I've had two pigs that developed abscesses on the jawline, both puffed up very abruptly, although at least one of them had obvious issues with her teeth before the abscess puffed up, with difficulty chewing, weight loss, a couple of dental trims, etc.) Abscesses generally need to be lanced and drained, they will not clear up in guinea pigs just with antibiotics as the pus is so thick and hard to clear. The vet can assess the other lump under her leg as well. Abscesses can be serious in guinea pig, but can be treated effectively with a knowledgeable vet and good care. Sometime it's possible to remove the entire abscess capsule so there is no aftercare required, but most times (and both times when I had a pig with a facial abscess) the abscess was drained and left open to continue to draining so I could irrigate the wound and express any pus that came to the surface and allow it to heal on the inside out with time and antibiotics. One of my pigs unfortunately passed away after getting sepsis from a tooth root abscess, but I realized after the fact that the vet was not up-to-date with his meds and I think he also clipped her teeth improperly at the same time and left her unable to eat. He also gave her barely any antibiotics and did not give me good instructions for how to syringe-feed and clean the wound and, being a new owner, I had no idea what to do. My other pig made a full recovery with some antibiotics and aftercare- she had her abscess lanced at about 2.5 years of age and is now turning 6 this month without it being a problem again. Hope this helps a bit- definitely see the vet!