No vitamin C for a kitty ok? In fact, recent science has shown it's not that helpful in humans either (it's a good deal 'power of suggestion', which won't work in a cat). Also, please don't put anything in her eyes. Use plain, warm water to wipe them off, or a 1/2 and 1/2 hydrogen peroxide + water solution, or a simple saline wash (not in the eyes, but just to remove the crust and discharge).
Chances are this is an Upper Respiratory Infection. These are usually viral, but they may have secondary infections of bacteria (even fungal or parasites). Since it could spread to other systems, turn into pneumonia or possibly more, it's always the safest suggestion to have a vet evaluation to determine the cause so it can be properly treated. Colored discharge (mucus) from the nose or eyes is often indicative of a bacterial problem.
Now, given that these infections are usually viral, you should know that there are no treatments for viral conditions, just for the possible secondary bacterial infection that may be present.
Look here for more info about what happens http://www.marvistavet.com/html/body_feline_upper_respiratory.html
The good news is that if your cat is still eating, using the litter box normally, does not have a fever (how to take the temp and what is normal www.petplace.com/cats/how-to-take-your-cat-s-temperature/page1.aspx if there is no labored or difficulty breathing, loss of balance, persistent vomiting (or any vomiting/diarrhea with blood), you can probably wait.
To encourage eating and hydration, use a particularly smelly soft/canned food, preferably with ‘chicken', ‘beef', etc. listed in the first two ingredients rather than some vegetable product or meat ‘by-product'.
If kitty stops eating/drinking completely, vomits bile or foam, has diarrhea, any blood from either end, mucous becomes yellow, green or yellowish-green, or you just ‘know' (trust your instincts) something's not right - make an emergency visit. Most vets have emergency care numbers, will open their office especially for emergencies or direct you to an emergency care clinic.
Also, if this doesn't resolve in 5 to 7 days, kitty needs to be seen.
Setting up a vaporizer without meds in it is often helpful for breathing.
A heat source helps too (I prefer non-electric options).
Use a thick, clean sock and fill it ¾ with plain, raw white rice. Knot the end and microwave it for about 1 ½ minutes. Shake it afterwards to distribute the heat and be sure it's not too hot.
Rice socks can be used on people too for muscle aches and pains.