It has to be a vet appointment I'm afraid to have a proper look. If you are worried about her eating it is important to start daily weighing to make sure she is not losing weight because she is still very young. Have you had them a long time and are they the same age?
Is your boy normally aggressive towards your girl? If there are regular disagreements it could be that they don't actually like each other and would be better in separate enclosures. It can happen - I got 2 girls as company for my neutered boy thinking they would all get on but one of them hated him and attacked him! They could not live together - he was very frightened - but they were neighbours through the bars. If yours are normally friendly with each other I suppose it could always have been an accident or she might have caught her mouth on something in the cage? If they are friendly she will take comfort from his presence while she is unwell and to be honest if they were actively fighting I think you would have noticed something?
If the other one were female I would understand more about the wound as females have a habit of kicking out backwards when surprised from behind and the piggy at the back can be scratched by a claw by mistake. They will also spray pee into the eye of another pig that gets too close!
There is also the possibility of a fungal infection (we call it 'Ringworm' - but it's not a worm, it's definitely fungus) that can cause intense itching and it commonly shows up as scabbing and hair loss around the face, eyes, nose etc. They are uncomfortable and scratch till they bleed so if she has this she might have done it to herself and she would be repeatedly scratching at the same spot so the wound would not heal up as you'd expect if it was just a scratch. It is treatable but you have to treat both piggies and also be careful yourself as ringworm can be spread to humans - and then back to piggies! My son caught ringworm by getting a tiny scratch from the nail of one of our first pigs - for the child it was easily treated with a cream and he had no symptoms other than a red ring-shaped rash around the little scratch... very characteristic. More difficult to treat the piggies because they are so furry! But if that is your diagnosis from the vet the forum has a very useful guide about treating and cleaning to help prevent the spread. If you have a chance to take a photo you can attach it into a post on here so the health experts can compare it to other facial wounds they have seen.
The lack of squeaking might be a coincidence but if she is unhappy, frightened by her companion, in pain or just desperately itching all the time she will not feel herself. She might appear less active. When mine are properly ill their ears seem to sag but it's hard to spot as piggies hide their illnesses very well.
The final point I have to make out of duty. You have not mentioned whether either piggy has been sterilised (I know some countries can neuter the males at 3 weeks) and the forum will never support intentional breeding as it can lead to such stress on the females. So I am duty-bound to say that if both piggies are fertile they should not be together at all but in secure cages next to each other where they can see, hear, smell and even make nose contact but where they are safely apart. Are you very sure you have a boy and a girl? If your male is the same age as she is they are both fertile and she may well already be pregnant - they are very efficient breeders - but she is very young. Supporting such a young piggy if she is pregnant and if you have possibility of ringworm (which might have taken hold due to the stress on her body) is for those here with more experience than me. The pregnancies last about 10 weeks I think and it is difficult to spot until the very end when they are almost ready to pop. Please think carefully about these last comments for the sake of your piggies - and I apologise if I have misunderstood anything about the situation.
What a long post! So sorry - but in summary:
Tell vet when injury first appeared and ask about accident or bite or maybe ringworm possibility or just infected wound? Vet might also want to examine your other pig for any sign of ringworm or fighting damage.
Tell vet about wheeking loss and weight loss or gain and any other change in symptom or behaviour - even if it seems silly.
Tell vet if there is
any chance of pregnancy as normal physical examination of guinea-pig might be uncomfortable or even cause harm to any babies inside.
Good luck with the vet visit and keep us informed... we'll keep everything crossed for you here
Oh and if you can keep everything all together in this thread about your piggies it will help people keep an eye on all the different aspects of your situation so they can support you for as long as you need x
