Your girlfriend as the “House Master” has a duty to register a TM30 report within 24 hours of each arrival. She can do this online and you can take a screen print of the registration to immigration. They need the code for the address (allocated when you register), so make sure that the page that you print contains that.
on the 3 occasions I have been asked to prove proof of funds, I have been able to open the K-bank app and shown a balance in excess of 20,000฿. Never once have they demanded to see cash (although I could have easily walked back to an airside ATM and withdrawn it). This has been at Don Mueang and Suvarnabhumi. Never been asked at Phuket.