Tourist L visa to visit girlfriends family - invitation letter help!

Hi

I'm going to China for the first time to meet my girlfriend's family. My girlfriend is currently studying in the UK and we are both going together to China for 3 weeks. I've never made application (to anywhere) before and I'm getting confused by the instructions.

So I have my return flight tickets booked. Now I need to get the Tourist L. I think I need an invitation letter to stay with her family. Should this come from my girlfriend (as a Chinese citizen with her ID, but currently in the UK) or from her parents, who are also citizens, but the relationship between them and myself is more difficult to describe in the invitation letter. Several samples I have seen online say the inviter needs to describe the relationship with the invitee (me).

Hope that makes sense.

Thanks for the help!