No one mentioned the subject of money, but I was quite surprised by the differences and hidden costs. Since I bought DVC first, I had assumed that Marriott would be the same arrangement, but that was not correct. I would not purchase Marriott directly from the company, since most of their properties can be bought on resale for much less, and your friend does need to consider that she may lose money if she later sells the timeshare. Disney's price has continued to rise, so it is less likely in the short run that your friend would lose money.
There are hidden costs associated with Marriott. Trades to other Marriott resorts are not free, you pay Interval to list your timeshare for trade, and again when they make the trade. I think I paid $169, besides the cost to join Interval. While it's not a lot of money, the cost will add up over time, and needs to be considered. Another problem for me is the lack of flexibility with Marriott--you usually stay for a week, if you can only stay 5 or 6 nights, you just lose the oher night, and most reservations are Saturday to Saturday, other configurations are difficult for them to deal with. With Disney you can stay for 2 nights or 20 nights, if you have the points, so the flexibility is far greater. Nevertheless, if you are buying Marriott to trade, it always trades well, and the company has resorts all over the world, so travel is much easier with Marriott than Disney. Marriott resorts are each a week's trade, no matter where I trade to, but with Disney the DVC resorts are quite cheap on points but when trading out it takes an outrageous amount of points to stay a week at resorts that may be nice but not NICE, if you know what I mean. It had taken me awhile to understand, but I would say that Marriott is nice if you want to travel all over, but DVC is the way to go if you return to Disney year after year. It all depends upon a person's vacation habits.