Well, if they are going to get married at Disney with 30 guests, Disney would consider it a custom wedding.
For some background, a custom wedding is a wedding with more than eight guests. If you have more than eight guests, it becomes a custom.
That being said, to have a custom wedding at WDW, you have to spend a minimum of $7500, if it is held on Mon-Thurs. For a Friday, St, or Sun wedding, you must spend at least $10,000. Of course, this does not include things such as the wedding gown and tuxes, but they can handle just about everything else.
You also have to guarantee a minimum number of room nights at their resorts. They base the number on the number of guests you have. Most people worry when they hear this, but then, a lot find that they don't have much trouble fulfilling the obligation.
Anyway, I am not a complete expert, but there are two websites you should definetly look at for more Disney wedding info. They are
www.disneyweddings.com (this is the official Disney wedding site) and
www.yourfairytale.com (this is an unofficial site, with lots of info.)
Have fun whatever you (or she) do, and I hope this was helpful!
-Aurora