Advice on gaining the trust of my girlfriends mum?

im 16 and been going out with my girlfriend for 2 months now. and she stays at mine til late on a saturday and i suggested maybe her staying over. her mum just laughed sarcastically. when shes at mine she doesnt wana leave and gets really down. n tbh i feel like **** wen shes gone aswell. i enjoy being with her and spending time with her. but what can i do to convince her mum im not just some shallow twat looking to get my dick wet? i was thinking of like sitting down with her mum and telling her how i feel bout my gf etc. but my girlfriend said she would find it emarressing. so im kinda stuck :S any ideas?Advice on gaining the trust of my girlfriends mum?
i am a female and 16, and have 2 serious relationships, and sorry but it is just the way girls mums are. mine was very protective. and only let me stay at my boyfriends, the 2nd relationship, after 4 months when she knew it was starting to get somewhere. but it would always be on another room .maybe stay at hers first so her mum can see that nothing is going on. and gain her trust. but my mum never let us alone or anything and hated us going upstairs. it is just somthing you are gong to have to do. and try and get the house to yourself at yours ;)