Melissa Cochran, 46, suffered a broken leg and rib and a cut to her head after Khalid Masood drove into pedestrians on Westminster Bridge on March 22.
He killed four people, including her husband Kurt, 54, before stabbing a policeman to death outside Parliament.
The couple, from Salt Lake City, Utah, had been visiting London to celebrate their 25th wedding anniversary.
Doctors cleared Mrs Cochran to fly back home last week, her brother Clint Payne said.
He added that Mrs Cochran, who was in a wheelchair when she joined a service for the families and survivors of the attack at Westminster Abbey on 5 April, was healing faster than expected.
The other people killed on the bridge were Aysha Frade, 44, who worked at a London sixth-form college; retired window cleaner Leslie Rhodes, 75, from south London, and Romanian tourist Andreea Cristea, 31.
PC Keith Palmer, 48, who was married with a five-year-old daughter, was killed in the forecourt of the Palace of Westminster, before Masood was shot dead by a police officer.
Mr Cochran, who ran a recording studio, died at the scene on Westminster Bridge from multiple injuries.
The couple, who were on their first trip aboard and visited other cities in Europe before arriving in London, had been due to return to the US the day after the attack.
They were also spending time with Mrs Cochran's parents, who work at a Church of Jesus Christ of Latter-day Saints mission.
In an interview with the BBC, Mrs Cochran described her husband as the love of her life, and said she does not feel "any ill will" towards Masood.
Mrs Cochran recalled "the panic of not being able to see my husband anywhere" after the attack, and how she learned of Kurt's death.
"I had come out of recovery and they placed me in a hospital room. My parents had come to visit and were there waiting for me when I came out and I had asked them to find out what had happened to my husband.
"Previously to that no-one could tell me... no-one had any information. My parents walked out of the room and came back in.  Both grabbed my hand and said that he didn't make it, which crushed me."
The injured wife of a man killed in the Westminster terror attack has flown home to the US.