Please have the eye checked in case it is an ulcer on the eye surface from an eye injury; that is treatable with eye drops and gels. The sooner it is treated, the better as eye injuries can deteriorate quickly.
If it is a cataract (in rare cases a guinea pig can be born with them), then there is nothing you can do. However, it is a matter of training and working out things to enable her to live a normal life.
Use a constant flow of talk to alert your girl that you are in the room and create different "melodies" for each regular ritual. Train yourself to form pictures in your mind about what you are going to do around and with your piggies. Use guinea pig body language to reassure your little girl and to make friends with her.
I would recommend to feed any pellets and veg in a bowl each in portions that can be eaten in one go 2-3 time a day to make sure that she is getting her fair share. Up to 80% of the daily food intake should be hay. Make sure that you have plenty of hideys; ideally one for each piggy and - if possible - one extra. If you are worried about bullying, make sure that they all have two exits. Rub any new furniture with a rag that you have wiped on used furniture. Blind piggies orientate themselves mainly be smell and hearing, which are both sharper than our human senses anyway (unlike sight in guinea pigs). Contrary to mos advice you'll find, blind guinea pigs cope well with changes to the layout as long as you cater for their sense of smell.
You may also want to have her checked for deafness by your vet, just in case.
You may find these links here from cataract piggies of mine comforting. I've had a number of them, and at some point had a dedicated group that still had their free roaming time on the floor, lawn time and shallow ramps in their cage.
This is a little picture story about my cataract sow Mischief:
Turning a blind eye on mischief - another piggy story
And this is a video about old (and somewhat arthritic) blind lady Mali still enjoying herself. She'd only just discovered a new loop two days before her heart suddenly gave out at 8 years old.
The Excellent Adventure Sanctuary looks after several blind/deaf true albino guinea pigs with dental issues (so called lethals). You can find lots of videos on their facebook page.
The Excellent Adventure Sanctuary (for guinea pigs with extra needs)