Oh, this girl sounds like she is in need of some serious help!!!!!

I agree with the suggestion to contact her parents or anyone else who is close to her- a friend or someone (ANYONE BUT YOU!!), and attempt to get this girl help.

She is obviously going to huge lengths to fabricate the whole thing- and from how you have described her- i wouldnt be suprised if she didnt start beleiving her own lies!!! Which will get very dangerous for her!!

You mentioned the script (well spotted on the spelling Lulu!!) may have been for anti depressants. i have a friend who needed to take a form of antidepressant, and she was strongly encouraged to STOP taking them when she wanted to get pregnant. I am not saying that you CANT neccessarily take them while pregnant,(there are probably special ones- another thing to quiz her on- do a little research and find out which ones a Dr would prescribe to a pregnant lady and see if she answers right!! ) but i couldnt see a Dr confirming a preg test and setting you up with a script for drugs that could possibly cause harm to your baby in the one visit!!

(WARNING GETS A TAD TOO MUCH GROSS INFORMATION)
Another thing to note- have we established she may still be on the pill??? I know that you can skip your periods while you are taking the pill, you just keep taking the pill/pills and miss the sugar ones- so if she has been living with you- over the last few months or she can somehow "confirm" she hasnt had a period- this could be her way of doing it. (It can be a tad hard to hide that time of the month if you are living with someone or having close contact) She wont have had any bleeding- also, if/when she does happen to "miscarry" (the only easy way out of this lie) if she hasnt bled for a few months coz she was skipping her period- her bleeding WILL be slightly heavier, clotty and easily passed off as a m/c. Just a thought incase she goes down that road for the sympathy side of things.

I just realised how close i can be to thinking like a physco when i put some thought into it!! LoL!!! Scary!!!

I think we have pretty much established she aint up the duff, but what do you do now??? Play it out and see how she keeps it going? Or continue to hassle her into telling the truth?? I would possibly give it one more shot at nicely explaining that you simply do not beleive she is pregnant, and until she has proof (i.e. an ultra sound picture or better yet a screaming child in her arms) that you dont want anything to do with her.

Goodluck, and PUH-Lease let us know how you go- this is sooo much like a sad soap opera that i am totally hooked!! I am just sorry you are living this!! It will teach you to keep it in your pants in the future maybe!! Or at least USE PROTECTION!!! LoL!!!