She could put that in the will but the problem is that the provision is not enforceable. Once the home is distributed to the kids from the estate the will has no control over the property; it is up to the owners to decide what to do with it. The good news is that in order to sell it all the siblings need to agree and if you are one of the owners you can drag things out at least a few months, time enough for you to get out.
The problem would be if the estate needs to sell the house to pay estate debts. If it needs to do that, the executor may sell the house notwithstanding whatever provision the will says about the timing of the sale, and it is possible that the sale could be concluded fairly quickly. Not much you can do to slow things in that instance.

