Basically, it seems as if she's not afraid to let everyone know you're together. That is definitely a good thing, she also feels protected and safe around you. Keep doing what you're doing and your relationship with her should turn out pretty substantial.
Yes it is a good thing cause the girl feels confident enough that your worthy to show to her friend; without getting embarrassed.
How long have you guys been together?
Of course it is. It means she's accepted you into her social life and would love for everyone to know about it.
Good thing as what Solidify said.