Megan, 30 – who played Katie Fitch in the hit E4 series, alongside Kathryn as the character's twin Emily – thanked fans for their support after she was granted permission to fly to the US amid the coronavirus pandemic.
Megan shared on social media: "Yesterday I was approved to travel to New York to see @k.prescott77.
Watch: Actress Kathryn Prescott hit by cement truck in NYC: ‘She is incredibly lucky to be alive’
"I can’t thank everyone enough for all their help and support in this and I really don’t think I would have made it to Kat without the amazing support I have received.
"I will be able to be with Kathryn tomorrow and that is absolutely amazing but please take a minute to think about what’s happening to so many others right now who don’t have the luxury of so much support and who can’t get to their families. I am incredibly lucky but so many others won’t be."
Kathryn – also known for her work in MTV's Finding Carter, 24: Legacy and films To The Bone and A Dog's Journey – was hit by a cement truck while crossing the road in New York City.
She has undergone complex surgery after suffering a broken pelvis in two places and injuries to both of her legs, her foot and her left hand.
Megan said her sister is "incredibly lucky to be alive", and had, "narrowly avoided paralysis."
The New York Police Department confirmed the incident to Yahoo Entertainment.
A spokeswoman said: "A preliminary investigation determined that a Concrete Mixer truck being operated by a 55-year-old male, was traveling on Bergen Avenue and attempting to make a right turn onto Vanderbilt Avenue when a 30-year-old attempted to cross the street and was struck.
"The pedestrian suffered injuries to both legs, both arms and a possible head injury. EMS also responded and transported the aided female to Methodist Hospital conscious and alert. The operator of the concrete mixer truck was issued a summons for Failing to Yield to a Pedestrian."
Meanwhile, the twins' brother Ben has raised over £4,000 via a GoFundMe drive to pay for travel to support Kathryn.
Kathryn and Megan's parents in Skins were played by John Bishop and Ronni Ancona. They starred in series three and four of the teen comedy-drama, which aired in 2009 and 2010.
Watch: Kathryn Prescott's top Skins scenes