A few more thoughts: when did your snake shed last? Is she due to shed?
I ask because they shed the outer lining of their nostrils, and sometimes a bit of shed skin fails to come out, causing a little blockage & thus a little noisy breathing.
Also, if your snake is going INTO a shed cycle, they can make a little noise breathing but actually be fine...if it's not bad, you might want to wait & see if this issue
"self-corrects".
The additional heat mat on the "cool" side may also help if it truly is the beginning of an RI. Stay vigilant...you already know what to look for (bubbles, mucus, etc).
Do you hear the slight wheeze when she is at rest in her cage (not being held) or only when you are holding her? Sometimes being held can cause an exhale that
may sound like a minor RI but it isn't...it's just the result of pressure on their long narrow lung when they're held & their body is "folded".
I don't really hear any noises when she is in her cage. She is in a rack, I only notice when handling.
She las shed on October 24th. It was all in one peice.