What?
That's the least evidence of her being a lesbian I could ever think of...
She has some VERY VERY good girl mates, ie they hug sooo much. - Most girls do this.
She performed a song at open mic night, she wrote about being a 'good girl'. - And...?
Worryingly comfortable chatting to my most perverted of mates without ANY flirt. - Maybe she isn't into flirting with complete pervs.
Still seems oblivious to my feelings after I've asked her round my house/to a gig/for mobile/for email address. - Maybe she thinks you're just being friendly, or doesn't get hints, or doesn't fancy you (which funnily enough, doesn't make her a lesbian)
None of my mates like her - So? Everyone likes different people, variety and all that...
Doesn't 'do' text, and never checks email - Maybe is a bit of a technophobe. And no, not all lesbians are afraid of mobile phones/computers
My mates gf -who I normally won't trust anything from- thinks she's a lesbian too. - You're listening to the opinion of someone you wouldn't normally trust?
Overall, I think you should strap on a pair and just ask her out. Don't do the fake anger thing, it's not a good way to go. She'll probably think you're just a bit weird. Be cool, and humour's good, just make sure it's 'safe' humour until you get to know her better. And I think you should grow up a bit too. None of those reasons you listed have anything to do with lesbianism. If she had sex with other women and not men/came out, THAT'S proof she's a lesbian. Otherwise, she sounds like a perfectly normally lass to me...
Good luck and all that. Hope it works out.