Long story short she is really interested in trying it and we have a big order of slime on its way from ebay, she's even been picking out outfits lol.
I'm still really nervous about talking to her about getting messy but its getting easier, will keep you all updated with how we get on when the slime arrives

Edit: kind of a pointless post I know but I figure if it helps somebody else work up the guts to tell their S/O about their fetish then its all good