In the process of selling....? Did she have contracts on both rental properties when she passed with only the closings left to be done? The problem you're going to have there is the stepped up basis wouldn't apply to the expectation of receiving money.
Here, you have executory contracts for fixed dollar amounts so there would be no stepped up basis for the amount of cash she would have received had she survived the closings. The real estate has been transformed from real property to anticipatory cash by virtue of the contracts.
Sorry for your loss.
