Thank you so much for your advice Dr. Loretta.
We've already tried the plug ins, which didn't really have any effect unfortunately. I didn't think of medication for her, so we'll take her to the doctors this week, and see if they can help.
She's never been too friendly with others even since we got her. When she was born the owner of her mother couldnt cope with the kittens (she had 6 kittens, and 2 young children herself to look after) and she had to put the kittens and her mother in a cattery from the age of 3/4 weeks til we got her around 6-8 weeks old. The only thing we cqan think of is something happened to her there, as i know the owner of her mother really well and Milo was the friendliest of all of the kittens when they were born. As she's got older she's just got worse though, and the main problem being she is a really pretty cat, and so people want to stroke/pet her!
We'll definitely get her to see a vet asap, and hopefully they can help with the anxiety she's got. Never heard of it before, so honestly thought it was something that we might have done, but we both love her so much, its just frustrating other people who visit us can't see what we see.
Thank you again for your advice,