Every time l enter the room and greet my 6 month old pup she rolls over on her back with enjoyment and urinates. Any ideas why she does this?

That sounds like submissive behaviour. The rolling on the back definitely is, and the urination probably is. I'd say your pet is still feeling intimidated by her new surroundings, and is trying very hard to establish that you are the one in charge. She may stop when she becomes more comfortable with her new home. If not, well, there may be some pet psychologists on this board that can give you advice.

I have had this pup for 4 months now as she does this with every family member, she seems to get super excited rolls over than urinates.