Definitely lame on the RF. If there is no heat or swelling it is likely a difficult internal structure which would be hard to heal, or its advanced arthritis, possibly even ringbone or navicular.
Wouldn't hurt to have the vet out to do some psychological tests on her, a basic flexion test and then get some suggestions on keeping her sound. If it is a soft tissue problem then it would be best to retire her to pasture completely, however with ringbone or arthritis it is good to keep them walking half an hour a few times a week, and on full turnout.
They say money doesn't buy happiness -- well happiness doesn't buy horses!