It sounds like Arwen is a really smart cookie. To say that about a sheltie, an already smart breed, means that she's got to be interesting to try to keep up with, since the intelligence in a dog can be used for good (making mom happy with perfect heels, bringing things, etc.) or evil. (thinking of ways to get what they shouldn't have, for example!)
I agree that potty training was being hindered by a dog showing a bad example to an impressionable younger dog.
I'm glad that she's made progress.
Would it help to have the fur between her toes trimmed, do you think?
Love All Life, Thank You For Posting! :)