If the lady was to die within 7 years of the transfer of the property, all or part of its value would count towards the total value of her estate when assessing the liability (if any) for inheritance Tax. After 7 years had passed, the value of the house wouldn't count towards the value of the estate.
However the foregoing only applies if the lady gives the house to her son 'without reservation'. If she continued to live in it she'd have to pay rent to her son (at the current market rates) or else have the house still count as part of her estate, for IHT purposes, when she died.
http://www.hmrc.gov.u...-home-to-children.htm
Many people believe that the '7 year rule' also applies when giving away their home in an attempt to avoid potential care home fees. That's not the case. Local authorities can go back for an unlimited period of time, still counting the home as part of the care home resident's assets, if they believe that an attempt has been made to 'beat the system':
http://www.direct.gov...CareHomes/DG_10031523
Chris