
Hi Simonne
At 6 months she is still a baby and to be honest i wouldnt worry about her not barking at the door at least its peaceful :-)
Have you tried keeping her on a lead when you have visitors and ask them not to fuss her and just ignore her,then only reward her (softly) when she has settled down,then let her off the lead but if she is naughty put her back on her lead (no fuss or shouting just gently),no matter what anyone else thinks i really do think dogs need to learn to think,well if i do such and such then this happens,after all who on here hasnt been trained by our dogs ;-)
Keep her on an extendable lead while teaching her recall and reward her when she comes back,make it an amazing hugging session and a crafty treat so she is pleased to be with you,when she is doing it on an extendable you could invest in a horse lunge line and do it with more distance between you.
But being a bulldog she could just be the ignorant stubborn monsters that we love bulldogs for being.
There are quite a few forums now for the other types of bulldogs im sure mollmoo (excuse me if I have the name wrong) will point you in the right direction.
Best of luck with Lola.