I would be very hesitant to sell up. I have heard some horror stories and know a couple of families who sold up their land thinking they would be able to have a better future with money to buy this and that and invest in stuff. It didn't work out. There were no plans for a sustainable lifestyle, it was just the feeling of having a load of cash in hand. The money was gone very quickly and they were then worse off than before they sold the land. One family ended up renting land for farming to make a living, but at least they now have a house and a pickup truck. Sad, but not uncommon.
Money management skills, or rather lack thereof, seems to be a major problem in Thailand and is not taught by parents or in schools. As a result there is a massive personal loan and credit card debt problem here and just about every civil servant is in debt. Crazy situation.
Hold on to the farm Owl. It is also a great place for you to spend time with Mildred, feeding fish, planting this and that, teaching her about wildlife, plants, farming etc. and generally enjoying each others company outdoors.