Over 70 and selling part of garden

My mother is over 70 and would like to sell a portion of the garden of her home. What are the implications of this from a tax point of view. She is receiving the Old Age contibutory pension and has no other source of income. She has no other assets.

If its sold at above 'current use value', eg for a new planned house or likewise, she pays 20% CGT on the increased value of the land.
This tax is unconnected to other taxes or benifits, so her status is pensioner etc is not relevant.