You need to get your dog back to the vet. If this is not an option tonight, try to go first thing tomorrow.
Concerns include infection and leaking of the stomach incision. Taking her temperature and checking the gums/capillary refill time (CRT) would tell you if there is a fever, which would indicate infection, and the state of the circulatory system.
You can take the temperature using a human thermometer. Lubricate the end and put it in the rectum 1-2 inches using gentle pressure. Remove it after a minute. Normal temperature for cats and dogs is 101 - 102.5. 103 is a low grade fever and 104-106 is the common range for fevers.
Look at the gums. They should be pink, not white, blue or bright red. Press on the gums behind an upper canine tooth using your finger. It will blanch white with the pressure and be white when you first remove your finger. It should return to pink in 2 seconds or less. If it takes more than 3 seconds, it indicates poor circulation, which can be caused by dehydration or heart problems.
If the temperature, gum color and capillary refill time are not normal, you she should be seen as soon as practical.
Let me know if you have follow up questions.