Thanks for the rating although I think you may have been premature in clicking on the icon. Hopefully, I'll deserve it with the following information.
I'm not certain as to what drugs you'll have available to you in the UK as opposed to those here in the States but, hopefully, there will be some commonalities.
1. Use warm water to clean the eyes and nose of any discharge that builds up. Over the counter artificial tears can be used to flush out the eyes.
2. Nasal decongestant drops can be helpful although many cats don’t like them very much as you can imagine. The medicated ones (a-c below) should only be used for three days in a row, with one drop in each nostril; otherwise what’s known as a rebound effect may occur. This is one reason why I prefer "d":
a. Pediatric otrivin=0.05% xylometazoline
b. “Little Noses" Decongestant Nose Drops with phenylephrine hydrochloride
c. Afrin (oxymetazoline)
d. "Little Noses" Saline Spray/Drops non medicated which can be used more than three days in a row.
3. You can place her in a bathroom with hot water running so that the steam can loosen up secretions although this is pretty wasteful. A humidifier can also be used in a small room.
4. Force feeding is sometimes necessary in these cats if they aren’t eating although it sounds like this won't be necessary. But, just in case you might need to supplement her, you can mix canned food (or human baby food but avoid onion and garlic formulations) with a lot of water in a blender and use an eye dropper or syringe to squirt some of this liquid into side of her mouth.
5. Probiotics such as Forti Flora have been shown to help many of these cats with URI's; probiotics aren’t just useful for gastrointestinal issues. This particular product is available as a powder which is sprinkled on the food every day and can be purchased at many pet/grain stores (at least that's true here in the States) or online.
I hope this helps. Deb