cat has been drooling past couple days and its bad right now

bella is 12 years old. just had her annual vet visit where they had us give her an arthritis supplement (cosequin), start using Vetoquinol viralys powder (used it a while ago with my other cat and nothing went wrong), changing over the cats food so a little of each mixed in. she has no behavior changes except that you can tell she’s uncomfortable because poor girl has to keep her mouth open. i watched her jump on the couch, she was purring when i was brushing her, she’s laying on her side and headbutting us for pets. ive been cleaning up her drool, the last few pictures were when i didnt clean her up for 10-15 mins. called the vet and they told me to stop the new joint supplement. i also am stopping the viralys powder today. i plan on calling her vet again tommorow and getting her an appointment. im scared for her though, never had anything like this. any advice how to make her comfortable?