Are you aware that by letting her have free roam of the house you may be keeping her sicker longer? Unless you are following her around all day and wiping things down after her, you may be allowing her to reinfect herself having so much access to the rest of the house.

Your best bet would be to confine her to either one room OR a large kittening pen. So you can wipe down the area with dettol kitchen spray (not dettol concentrate or Flash)OR even better Safe4 spray, Vetaclean or Trigene if you can get some online or from your vets.

You also need to clean the soiled areas with a bio washing powder solution leave to dry and white spirit also leave to dry(vodka, gin, the cheap stuff is fine!). Using ammonia or bleach based products will only attract them back later.

It's more likely she is not using the tray because she doesn't feel well NOT because she can't smell the tray. Cats used their litter trays by habit not just by smell. She's just unwell and trying to tell you this. Keep her confined to a smaller space and clean up regularly and she will be fine. You also need to keep her away from the other cat as even if he doesn't show any symptoms he can pass it back to her again as a carrier. Quarantine is the key with keeping the sick period down to a minimum. With the right care and cleaning you can get it to 4-6 days! Don't forget you can be part of this infection spreading so wash, and change your clothes or wear gloves and a plastic apron when cleaning and treating her.

Don't place the Olbas oil directly on her skin. you can put her in a small dog cage and cover it with a towel with a bowl of hot water and Olbas oil next to the cage but please do not place it on her skin or coat directly or leave the bowl in the cage with her. 15mins is max for leaving her with the hot water bowl twice a day. Early AM and before bed I find is best for them.

Leaving her to rest and be in a Large dog crate or Kittening pen is ideal. The more she stays put and get some sleep and doesn't get too over heated the better. With the pen and crate you should have enough room for, food, water, bed and litter tray. That should be it! She'll be back to her old self in no time! Good luck hope she feels better soon.