Usually if a guinea pig is loosing weight and has a wet chin, then it's a dental problem.
It's not usually an incisor problem though- it's usually a problem with the molar teeth (which you can't see without a special scope).
These can become overgrown and then rub on the tongue and cheeks, causing the guinea pig to drool.
My advise would be to get these molar teeth checked at your vets- as if it is them, the sooner they are burred down (sedation is required) then the better for her.
Very difficult without the correct tools that for sure!!
The sedation is pretty easy- there's lots of options for that from a sniff of gas to injectable drugs, however, you do need the correct dental equipment, and preferably a 'dental burr' to burr down the overgrown molars- so ideall you will need to find a small animal vet that deals with rabbits and rodents. Although if you can't find a vet that does have a dental burr, then a rasp (to rasp off the sharp edges) is better than nothing.