Everybody else already gave a lot of good reasons why it's not a good idea, but here's a couple more to think about that haven't been mentioned:
1. Your dog can not drink water.
2. She is still feeling anxious. The mouth is not the only destructive part of a dog. We fostered a shepherd with extremely severe SA for a while. She had to stay on a tie out because she destroyed her steel drop pin crate and bit through a wood and glass door to try and follow us. While on the tie out she managed to back herself up to the garden hose nozzle, which was a good 6 feet out of reach of her just standing there, turn it on with her back feet, then shred the hose itself with her back paws. It was horrifying.
I have seen SA dogs literally dig through layers of drywall, carpet, linoleum, wood flooring and concrete to try and escape and find their owners. They will dig until their paws are clawless with bloody nubs for fingers.
If you take away your dogs ability to chew without addressing the anxiety, I guarantee you will see other, worse destructive behaviors surface.
3. Some dogs become adept at removing their muzzles. If you leave it on for long periods unsupervised, this is likely to happen.