When they're young you should take them out every 1hr to see if they have to go.. this will reinforce where they should be going.
When Belle starts to go say your command like "go poddy" or "go to the bathroom", and do this EVERY TIME. Eventually Belle will go on command.
It took Moose a while to get it too so don't worry it's just not your dog.
The thing to remember is they won't ever get poddy training if you don't constantly reinforce the same thing over and over.
Training them this is a LOT of work and takes a LOT of time.
Once you get that command in their head and they listen it maeks your life EASIER, and once you learn their "schedule" it's even easier.
For instance, with Moose I wake up, check email, he hangs out with me then I feed him and I mix water in his food (very little). Then I take him out to go Pee, and he comes back in and rests with me for 1hr-2hrs then I take him for a run or walk and during that time I KNOW he will Poop. Then he gets more water, and either hangs with me while I work or outside with me exploring... he gets water throughout the day, and I let him go out when I thnk he needs to. He gets real ansy, and will nudge my hand, or put his face on my lap if I`m on the couch if he wants to go out, moose is not a dog that goest ot he door so it sucks in that aspect, but he does try to get my attention, and says HEY I NEED YOU. (Since I take him out often anyway this is rare now-days). He poops once a day unless I run him again later after his nightly feeding, which is rare because he nromally has diahree if I run him after dinner, so after dinnner he gets a littlew ater (feed is aruond 6:30ish) and then I let him Pee once before I put him down for the night.. Depending how tired he is he sometimes goes to bed at 7 or 8 and sleeps until 9 the next morning.