Two thoughts:
First, when and where did your MIL buy? If she is still within her rescission period, she should rescind and do some due diligence to make sure this is right for her. If she decides it is, I'm sure the people who sold it to her would re-write the same contract. But, better to be informed than surprised down the road.
Second: Using RCI is not nearly as easy as it sounds, and certainly not as easy as the sales person made it seem. You don't just get on the site and book something like it was a hotel. Instead, think of it like a big barter system. You deposit some vacation time into the system, and you get some credits back. Those credits are sometimes called "trade power units" or TPUs. Then, when other people deposit their vacation time, you can spend your credits to book it. But, (a) you can't book something until someone else deposits it and (b) things in high-demand cost more credits than most people are given for their time.
As to point (a): DVC deposits much less than they used to. As noted, almost all of the deposited weeks are 1BR SSR units. You should consider 2BR units impossible for the moment, and you should also consider any of the "near-park" resorts (BCV, BWV, BLT, GFV, PVB, and maybe VWL) so unlikely as to be impossible. You will also have to have nerves of steel if you are a planner, because DVC tends to deposit quite close to check-in date, somewhere between 1.5 months and 4.5 months prior, maybe a little more. So, well after your 180-day mark, and possibly after your 60-day mark. My most recent exchange was confirmed only 73 days before check-in, just barely enough time to get my Disney Resort reservation number for 60-day FP+ reservations. Finally, there are times of the year when exchanges are very hard to get---mid October, early December, a few others. That most recent exchange started during the Princess race weekend, and I had a backup planned, just in case, because I was not sure I'd get it.
As to point (b): depending on what your MIL bought, she may or may not have sufficient TPU to book a Disney deposit. Most people have to combine two (or more) of their own weeks to get one of Disney's. However, this can really vary depending on what she bought, and the folks at TUG (tugbbs.com) can help you there.