Hi J.,
I'm really new to this site and have never posted anything, so please forgive me if I seem long-winded. I have a small dog (Toy Fox Terrier) currently, but have raised Golden Retrievers in the past. We had one that loved to dig in the garden, but after she learned some basic commands, we were able to teach her not to dig just by saying "No" in a firm tone each time we saw her start up. I think the response from the Chihuahua owner was on point-get your puppy into obedience classes so that she learns who's in charge and how to listen to you. Another trick that might work is this: As soon as you see her start to dig, give her a firm NO, and then hand her something appropriate to chew on, thus distracting her.
As for the feet wiping, we always brought the dogs just inside the door and told them to sit and stay. They each would wait to have their feet wiped clean, but again, that's a basic command that's usually learned in an obedience class. I know that Petco and PetSmart both offer low-cost puppy classes, but you might also find some good recomendations (sp?) from your veterinarian.
Good luck!
E.