Q. Lab keeps licking/nibbling her paw. No clear cut/sore just looks red and irritated. When or should I contact a vet?
A. You should have it checked to be sure there isn't a skin infection. It could also be an allergy to something.
If there's no infection and allergy it may be boredom and the irritation could be from the constant grooming. Some dogs will go as far as licking to the point of open wounds.
Rule out medical causes first, if those check clear, try increasing her exercise and be sure to give her mental stimulation as well. For that you can feed from puzzle toys or do some training.