I am sorry to hear that Mercy lost her bark after her grooming yesterday.
I suspect that she was very excited to be at the groomer and see all the other pets. It is very possible that she barked a lot more that usual, which can cause changes in her voice today. Some dogs also try to "catch" the air from the hair dryers and that leads to minor irritation and can dry out their respiratory tract.
As long as she is happy, playful, and eating and drinking well her voice should return over the next week or so.
It might help to feed soft foods, add broth or warm water to her foods, and encourage fluid intake by offering broth to drink and offer ice cubes to lick. The more fluids she takes in the better.
You can also give her a teaspoon of Manuka honey to lick up, which is a natural anti-inflammatory and antibacterial, a couple times a day.
Try to discourage her from trying to bark, that will only make the inflammation worse.
If her voice isn't coming back in 10 days or so she should see her veterinarian. They may choose to prescribe an anti-inflammatory.
Please let me know if you have any further questions.