Try to negotiate with the wedding department. I had originally booked with a travel agent, but my aunt is a member so we got a quote throught the membership department. The reality is that my TA offered a much better deal for our guest. The room rates were cheaper, transfers were included, etc.Because my family members want to book under my aunts membership I did a second contract with the membership wedding coordinator. She was able to combine the rooms of both bookings to count toward my room nights. When it all breaks down I am not getting anything extra for have a member wedding contract. They do offer the 20% off of wedding packages but I am doing the complimentary package so that doesn't help me at all. You have to keep in mind that this is your wedding not hers. Your guest are spending a lot of money and traveling very far to be apart of your special day. Not only that but she is spending considerably more to come as a single. If it is more affordable for her to book seperately I think you should be understanding of that. I dont think it is reasonable to expect your guest to pay more so that you can save money (something that I had to tell myself lol). Contact the membership department to see if you can get them to count her room in your group booking. Also try to find her a roommate (another friend or relative who is a single). I have two friends staying off sight because it is cheaper for them. That means that I may not make my room nights, and I may have to pay more. I also have to buy day passes for them to get onto the resort. In the end I rather pay more to have them there, than to make the trip unaffordable for them. It is my wedding so it is my financial responsibility. If she can rebook under your group (get a refund from the other company) offer to pay the $200 dollar difference. That makes thigns easy for your MOH and is much cheaper than you paying for a private event. But first I would try to negotiate with MP get them to match the rates of the TAs. Most importantly try not to get worked up, the funny thing about planning things is that often dont go as planned