I'm so sorry no one has answered you before now. Yes, 6 weeks old is way too young to be away from momma. Yorkie puppies should not go to their new home until after 12 weeks old. Long time breeder or not I would not call your breeder "reputable" simply based on her letting the puppy go at 6 weeks old.
Now that you have her at your home it is extremely important that she stay warm, out of drafts, not be over-tired by too much play or over handling and it's critical that hypoglycemia be prevented. Hypoglycemia is a huge risk to tiny puppies and even more a risk when they puppy is so young. Please research this and ways to prevent it. I would suggest that you get canned goats milk and mix with canned puppy food, feed a soupy mix of this 4-6 times a day as well as leaving dry puppy food out at all times. My favorite is Royal Canin puppy food since it's not too hard and it is so easy for babies to crunch up. I would also recommend you get a supplement called Nutrical to feed to your puppy. This supplement comes by other names but helps keep their blood sugar levels up.
Please keep us updated on how your little one is doing and feel free to email me or send a private message to me with any questions. Good luck
Teresa