Older cat with congestion.

First, thank u for your input on my cami that past on previous question.my husband had given her to me years ago but he passed 2yrs ago from cancer which made it even harder because it was like part of him again leaving but the bright side is I have my son and other animals I love dearly too..

My question now is on my older cat Prissy she is 13 and she sounds very very congested, runny nose at times I see her still licking nose and using paw to clean..you can constantly hear her breathing through her mouth very noisy at night when she sleeping. This has been going on a couple months I was hoping was allergies..I took her to the vet blood done first nothing major showing and they did a head scan that dr did not think anything like a turmor was there but he wanted to ask someone else that was more experienced in that field and he also agreed no tumor in head..but the luck I have with cats as u see not always good..when I went to pick prissy up dr had to anesthetic to do head xray..my cat had a reaction to this and was blind dr said first cat he had ever had this happen to that it was a very low dose and had only had a dog happen to one other time...well I took her home and prayed her vision would come back because dr didn't know if it would or be permanent....thank god Prissy vision was all back within 2 days....That's my dilemma dr said he would have to refer her to state vet that has equipment to do mri I think to try to diagnose more specifically...my vet gave her antibiotic/steroid shot and that worked for about 2weeks then it has all come back again and at times I see dried blood on nose..i try to clean for her and try to use salt/water saline but not as easy task...Any suggestions??..I know this could be something life threatning but if I go to state vet they will also have to put her to sleep to do xrays that my fear since her reation and she is overweigh 12/14 lbs. Have you had any experience with this would appreciate your knowledge...thank you again..carol