the shaking, not eating (although that happens with new fish sometimes), shyness (although not unusual for a new fish too), and the glimpse, and chin sound like she could be :thup:
watch her for a few days more - you will notice the chin getting darker blue/shaded looking and the chin will pop out and look sort of like a pelican with a full beak. I've seen good video recently that explained it well - i will try and find it and link you too - its a lot easier to see than read what you should look for!
how big is she/how old is she?