This "might" be a beginning RI...but do NOT under any circumstances use eucalyptus* or vapor rub for a snake, not ever. Watch, wait, & see if this worsens.
(*eucalyptus & other ingredients in vapor rub are very irritating to snake lungs, just like cedar is. It will make things worse.) There are some who believe
in using F10 to fog snakes for RI, but I've not used that, nor am I convinced. It's something you might look into & ask vet. I'm sure you know there are down-
sides to using antibiotics too? Not saying they aren't needed sometimes, but don't take any of these treatments lightly: "first do no harm". Also, keep in mind
that some snakes might mouth breathe & click a little if the skin in their nostrils didn't shed out with their latest shed, making it a bit harder for them to breathe.
Keep her humidity up & if she doesn't get worse, see if this improves after her next shed with you.
Expos are very stressful for the snakes...let her rest (sounds like her cage is fine) so her own immune system can function at its best best. I hope this passes.
She's lucky to have you on her side.And it's very UN-likely for a snake to catch anything from us...just don't give her "mouth to mouth", lol.
(Holding her mouth open a little might also be her trying or intending to hiss...her world has recently changed a lot & that's very scary for a snake.)