Super Gran (1985)

In a small British town lives an old lady who is making the best of her weak condition until small-time criminal mastermind The Scunner Campbell steals a new invention that he hopes will grant him superpowers--as soon as he makes it work. However, a botched firing makes the beam go astray and it hits the Granny instead. Suddenly, she gains super strength and speed to become the local superhero, Super Gran. Now, Supergran protects her town from the forces of evil, although The Scunner Campbell is not exactly a major challenge.