purring and pregant

Question
I have had a female cat come and live with me. It was abandon, I think and after two months of watching it dash out and pinch any scraps I had thrown out for the birds I realized it had no home  After giving it shelter from the weather and cold she finally came to stay. Is there any way I can tell if she is pregnant and if so what do I do? Just let nature take its course? I may be over feeding her as she licks the dish clean which is unusual for a cat. She must have been starving and makes sure she gets it all as iin her mind it  may be her last for a while.
The other question is why do cats purr? Is it , but they are 'alone' animal and it is strange they should want to share lol  

Answer
well if she is pregnant you can either take her to the vet and get her fixed or let her have the kittens. Cats purr because they are happy and i want to be loved on. just petting her will make her purr. And one thing youve got to know about cats is when you want to love on them, they dont want you, but when you dont want to love on them at the moment, they want love.