I'm glad it seems to feel a bit smaller. It's always good to avoid surgery if possible. There is always a risk with anesthesia (to every animal- humans included), but if it comes to that, it can be performed relatively safely on guinea pigs. It is important that the vet doing the anesthesia has experience with small animals and is using an inhaled gas (supposedly easier/quicker to reverse and much safer for small animals.) I'm always tense when my pigs have been put under, but my vet always reminds me that, although there is always a risk, in his experience guinea pigs do fine with inhaled anesthesia. Knock on wood, but all three of mine have been put out at one point in time... Linney had a large open abscess that wasn't healing removed from her lower back under GA, Frenzy had a large jawbone abscess on her face cleaned out under GA (she unfortunately later passed away due to complications from a major bone infection, but even in a pretty debilitated state she did quite well with the anesthesia), and Sundae... well, I've lost track of the times she's been out because conscious dentistry is not a thing here, but she's been put under at least three times and possibly four- mostly short dentals, but also to clean out a huge abscess deep into the jaw muscle, and she's done quite well with them as well. Just trying to give some reassurance that if you do end up needed more invasive treatment with GA, often pigs do very well with anesthesia. Talk to the vet to gauge their comfort level and experience level first, though. It's a case where I would much rather go with a vet who is accustomed to using general anesthetics on rodents than one who really is only experienced with dogs and cats!
my vet did say that aslong as the lump doesn't get bigger then she can't see any problem with it staying put til we're a bit better off. I was just worried about it affecting her health 
More grape size now x