In the short term you both should consider the possibility of a UK visit visa for her and maybe a Schengen Visa for Belgium at the same time. That way she'll have the freedom to visit Belgium with you during her UK visit. Just food for thought.

As you say Chris, the relationship is still early days but at least you know there's a free and rapid visa route for you both if ever you both agree to move it on to the next level.

As it stands right now it's just b/f & g/f and there's no country considers immigration on that basis.

Looking forward to following you story