The yawning and rubbing does make it sound like RI. The noise alone could be a million things. She is under 1000gm and stopped eating. She is unlikely sexually mature and equally unlikely to stop feeding due to mating drives possible but unlikely.

There is a few very simple things to look for take a speculum or credit card and open the mouth. It should look light pink to red much like a human mouth a bit lighter. There should be no bubbles of slime in it. Perhaps saliva but that should be thin not thick and sticky. I am sure you have had a cold or flu you know the difference between spit and phlegm.

If it is difficult to open the mouth you can very gently press under the chin towards the nose if there is slime in there often some will come out.

The time for the vet is when you start to think there maybe a possibility. RI caught early is easily treatable late it is life threatening and much harder to treat.

What are your temps like?
Hot spot (surface) ?
Cool spot (surface)?
Ambient air temps?

What is the enclosure like do you have good ventilation? If the room is dry do you need to mist?

It is possible that it is time for a vet visit. I would recommend a CULTURE be done. It will say there is or is not RI and if there is which antibiotic is the most effective.