My female cat has green liquid coming from her privates? Why?

DISGUSTING I KNOW! Just need a rough answer before I take her to the vets. I've noticed lots of green wet stuff around her 'private area' as she walks. She's also leaving it around were she sits, it is disgusting as she likes to sit on my bed and on top of our television sky box, and she is leaving horrible greenish white residue behind :// also I've not noticed an odour from it and she sits on my knee sometimes and I feel something wet and I love her and there's green wet on my legs! Also the fur around her is in big hard clumps and bits of her stones from her litter is sticking around there

It's a horrible question I know but I feel worried for her because I don't quite know what it is, I've never experienced this with my 2 other female cats, does anyone know what it is and what I can do to resolve it? thanks

NOTES * shes a couple months old, she's got short fur, she hasn't yet been to the vets as my parents haven't got round to it ( I don't need any lectures for that ) a few months ago she also was having intercourse with her brother a couple of times, again disgusting but we got him neutered