Chewing tail

[Changerazelea]

Our 18mo terrier is chewing on her tail and it is now red raw. Took her to the vet when we first noticed it on Saturday and she had glands squeezed as well as as an anti itch injections which was meant to last for a few days.
Due to the location on the tip of her tail the inflatable collar/cone doesn't preventing her from getting at it and since the injection has worn off she is going at it again.
I've tried a muzzle today and she has managed to get that off fairly quickly. Keeping it clean and have tried a balm which is meant to taste bad...she is undeterred.
Any other tips? At my wits end....
Thanks wise doghouse companions.

Back to vet I suggest. Must rule out medical first

either there is a skin problem or an infection, boredom or now a habit (bit like people who pick their skin about their fingers).

you could try an immediate no and put her down if she does it or lots of praise if she leaves it this might help
pethelpful.com/.amp/dogs/How-to-Stop-a-Dog-From-Biting-His-Tail

Depending on your dog's tail carriage I might look at something like a surgical body suit that I adapated to keep the tail covered (add extra material). You'll have to remove for toiletting but otherwise might help keep her off her tail until it heals.

Longer term I'd be looking at the following causes, in this order...
a) medical causes (as you are)
b) allergies (food and environmental)
c) sress and anxiety
d) boredom

Try cribbox spray. My trainer recommended it for chewing blankets. Very good. Is she stressed?

Thank you all for the replies. I managed to find a antiseptic powder from pets at home which healed it up nicely.