A vulnerable couple were forced to flee their home after a brother and sister stormed into the flat and demanded £240 in cash.
Judge Pamela Badley said Leonie Kinnish, 26, poses such a danger to the public that she must be given an extended sentence to protect the public from harm.
Preston Crown Court heard Leonie knew the couple, who were both in their 50s, had mobility problems.
At around 9.45pm on December 28, 2013, the woman went to answer the door of the flat in Mainway, Lancaster, and was faced with Adrian Kinnish.
The siblings barged past the woman and into the flat, where Adrian started assaulting the man, knocking him to the ground and kicking him in the body and head.
Leonie pushed the woman, who was using a crutch for support, and she fell to the floor before dragging her up and taking her to a bedroom where cash was kept.
The woman handed over the money and the siblings left the flat.
Leonie has previously served a four-year sentence for an unprovoked street assault with a hammer.
She was convicted of robbery and Adrian of assault causing actual bodily harm.
Adrian did not know his sister planned a robbery, the court heard.
After Leonie was handed her sentence, she begged Judge Badley to spare Adrian jail, saying: “Please don’t send him down. It’s my fault.”
Leonie, of Greenset Close, was handed a five-year custodial term with four-year extended licence and Adrian, of no fixed address, was given nine months.