Ok, now I have read over everything you have sent along and I do have to say that I am quite concerned about Bells.
As I am sure you can appreciate, the main avenues of concern with this type of exposure are respiratory and gastrointestinal/systemic. If it was sprayed everywhere there is a risk of ingestion due to her licking any oil that got on her paws. That said, given her breathing rate this sounds more like a respiratory based reaction. In cats, we can see respiratory irritation and inflammation secondary to high level exposures of airbone/spray products like this. It can inflame and thus narrow the airways leading to respiratory changes and compromise. And this is our concern here for Bells since that breathing rate is nearly twice normal for a cat at rest.
In this case, if you have not done so already, she needs to be relocated to a well ventilated room. We need to get her away from that concentrated peppermint and get her breathing as clean air as possible. Further to this, since we have an abnormally high breathing rate, we do also need to think about getting her vet involved. They can put her on oxygen if she isn't severely compromised (which gum color can give us a clue for), start her on bronchodilators and anti-inflammatories to open her airway and get her breathing easier. And I would note that while her appetite loss is the most visible sign, it is likely just a side effect of her needing to focus on breathing. Therefore, once we help her catch her breath, her appetite is likely to return.
Overall, poor Bells sounds to be having a respiratory reaction to the peppermint oil. Getting her somewhere with clean air is important but if she is breathing at twice her normal rate, we do want to get her vet involved for the above treatment to avoid her developing respiratory fatigue or crashing on us.
Please take care,