NoOnesGoingToEatYourEyes has a very good idea. Get them both to buy into the idea of a wedding WHEN SHE IS DONE WITH THE COURSE. Then you can safely wave them off into the sunset knowing that you have done your bit to secure their future.
Id also speak to your DD about whether she is struggling with the course work and looking for an "out", and what she hoped to achieve by faking a pregnancy.
Can you chat to the young man - see for yourself how he feels about it all? Maybe have a family meeting and discuss the logistics - the money owed on Y1 of course, the rent that has to be paid up front. Offer moral support but not financial for the wedding, make it clear that your preferred option is for her to wait 18 months until the course is complete. But ultimately, its her choice.
Once she is wed, I would withdraw your financial support - mobile contract, housing, allowance etc. In fact, Id be tempted to do that now, as she is going to be moving in with her bf and therefore will not need you - and you can then save a bit towards recouping costs of accomodation and course fees if she decides not to continue.
A short sharp shock of reality - having to work in a crappy job just to put food on the table and top up your phone - might be just what she needs.
I would try and establish why she is set on sabotaging her future though...maybe the reality of college has really scared her. The realities of uni and the volume of work, the dicipline needed to schedule and plan your own work, the difficulty of what you have to study. All these things could be causing a wobble, and making her want to run to the security and stability she knows - a married couple with a home of their own. But without mum and dad!