Bookkeeper popping in to agree with Swindler. Talk to a real estate attorney but also talk to a local real estate CPA (ideally one who also handles personal taxes in addition to real estate business tax). You'll want to know what the options are and what effects they can have in relation to her entire tax picture. Often a good niched CPA can refer to a good attorney and vice versa. It also doesn't hurt to talk to more than one. Most CPAs won't charge for an introductory/exploratory chat to see if you groove on them. Protip: if they're not willing to talk to you and your MIL in real words and insist on only using big accounting/legal terms, they're an ass. Move on to someone who's willing (and able) to talk like a regular human being.

Depending on how soon she wants to sell that land, though, keep in mind tax people are preparing for the busiest time of year. Either get a meeting set ASAP, or wait until May/June for an appointment.

She’s complaining about the cap gains. We told her to go see an accountant. Didn’t think about an attorney. Thanks.