Hi there! I'm sorry to hear that Emma is having digestive troubles - I know that it can be frustrating when your pet isn't feeling well.
Diarrhea in dogs can be something as simple as a self-limiting virus or an upset from a recent change in diet. In those cases, as long as the pet is acting normally and has a good appetite and no other symptoms are present, you can try feeding a bland diet of three parts boiled rice to one part boiled chicken for a few days. A bland diet can also be helpful for longer term diarrhea, but if it's been going on for more than a few days or if your pet is acting ill (ie: lethargic, not eating, vomiting, etc), then it's a very good idea to discuss the problem with your vet.
Since Emma has a chronic health condition, I would contact your vet as soon as you're able to discuss her diarrhea. In some cases if the Cushing's medication can cause diarrhea, and it needs to be adjusted ASAP to avoid potentially life-threatening consequences.
For chronic diarrheas, sometimes we recommend more "GI specific" blood work and fecal tests to try to sort out the cause. Sometimes a special prescription diet can be helpful as well. These are a couple of ideas to discuss with your vet when you speak to them next.
I sure hope that this helps!