That looks like a nasty temporal gland infection and yeah you need to take her to vet right away. You will most likely need injections and maybe have it drained and possibly cleaned daily. The vet may want to have the gland surgically removed too.
Looks like a mandibular abscess to me, though it is awfully close to the commisure of the mouth, so a temporal gland infection is also likely. My guess is that if you give it a squeeze (gently), thick white/yellow cottage cheese stuff will come out. If so, it will need to be debrided by a vet who will also put your cham on antibiotics. Even if it's not , it still needs to go to the vet.
Usually this can be secondary to a husbandry issue, though it could be secondary infection from trauma due to a fractious insect.
I'm glad your cham is eatting and looking fine right now, but remember, reptiles take a long time to get sick and even longer to heal. if you can fix it before the cham starts showing debilitation, you have a higher probability of fixing the problem (saving your chams life.)