well as i understand the law, if you were buying the house before she came along she wont get anything from it,this will be changed in the fututr though and then she will automatically get half of everything or a percentage depending on the situation.
If she has put items in your house for which she has paid for then theres a value on it and usually its half of what the item is worth.

You do get the first 30mins free at most solicitors now a days, as i used one just before x-mas in that time you can get a very very good idea of what crap youre about to jump in to.

This might help you: http://www.lawontheweb.co.uk/basics/cohabit.htm