Hi there and Welcome!
May I suggest you get some Nutrical to keep in the house... this is something you can use instead of the maple syrup for hypoclycemia and also it has nutrients in it for puppies that aren't eating well.... it can be found at Petsmart.. it is in a tube. It DOES work (we used it for Seymour when he was little because he wasn't a big eater.... actually he was very little when we got him... about 2 pounds at 16 weeks).
There are some very good foods out there for puppies. We feed Innova small bites at this time, we started out Shelby & Seymour on Royal Canin puppy small bites and they did well.... but Royal Canin had corn in it and the weight became an issue (they got chubby!). Sometimes there can be an issue with allergies and corn also.... but that was't the case with us... We have also fed Blue but it was difficult to get in our area which was kind of a pain in the butt to have to drive 40 minutes to get dogfood.
Seeger (our newest addition) started out on Innova and is doing well. We got him at about 14-15 weeks and now he is a little over 7 mos old. Still eating and growing!
I wish you good luck and hope that you find a good dog food that works for Bella! Keep us posted on her progress!