The Brussels griffon consistently ranks as one of the easiest dogs to train. As the AKC notes, they are “social, friendly, and easily trained and will usually get along well with other family pets and well-behaved children.” Just bear in mind they’re one of the more high-maintenance dog breeds because they prefer to stay close to their owners and don’t like being left alone.
Some dogs are slower to pick up house training than others. The important thing is to be consistent in her training. Re-read this guide and then check back with what you're doing. Has anything slipped, such as you don't stay outside with her or she goes too long between comfort breaks? Remember the golden rules which are to be there to praise her when she goes in the right spot and minimize the risk of accidents indoors
Choose a designated area for your puppy to "go" before bringing him home. This spot might be somewhere in the backyard, next to a structure that provides shelter from wind, or some other suitable place in the garden. Wherever it is, have a firm commitment to it before getting the puppy. You don't want to create inconsistent messages by shifting his toilet around the yard while you make up your mind.