German shepherd/Corgi mix

Question
My boss and I adopted a dog from the Humane society.  She stays at our shop during the day and goes to one of our homes at night and on weekends.  She is a very good dog, but recently she has started to tug/nip at our UPS driver and other customers' pant legs.  She doesn't do this to everyone and as far as our UPS driver goes, she did not used to do this to him.  It doesn't seem to be a mean action on her part.  Any ideas why this has started to be a problem? We have had her for about 7-8 Months now and she is around 5 Years old.
If I can ask another question about her anal glands. Hers seem to release A Lot.  She obviously doesn't have the opposite problem where we need to squeeze them but why does this happen so often?  Sometimes she is just sleeping under my desk and there they go - yuk!  She also seems to have the disgusting habit of licking the excretion off the floor.  She will lick for 5 minutes or more some time.  Why? and What can we do (if anything)?  
Thank you for your time.

Answer
Well it is probably a game for her,and sometimes dogs are weird around people in a uniform-now what is usually a good trick is to get him to give her treats,but only when she isn't acting up,as that will be praising her for it,what you do is put a chock chain and leash on her,and when she does that snap the leash back and say 'leave it' and when she finally stops acting up have the USP driver give her a treat so she sees him as a friend

As for her anal glands,that might be a questions for your vet,as I don't deal with medical problems-but i do know in some cases dogs can have anal glands removed if they cause the dog a lot of problems