Factually she is also a legal heir to you however the question of legal heir ship will not arise now.
If the property is your self acquired property or has been inherited by you as your share share in the partition deed or any other deed, it becomes your own and absolute property.
It is your will and wish to do anything with the property as per your desire. You can transfer the property by executing a settlement or gift deed in favor of your son even now over which no one can raise any objection.
If she is squatting in your property and refuses to leave you may lodge a complaint with the police stating that she threatens you to eliminate you with the help of goons in her side and also refusing to vacate the house but has been continuously creating nuisance and disturbance. Besides booking her under the provisions of IPC she can be booked for the offences for torturing the senior citizens under senior citizens protection act also.
You can file a civil suit for injunction also seeking relief of restraining her from interfering into the peaceful possession and enjoyment of your property and also for eviction.