The 25-year-old has signed a six-month contract with the club until 30th June, following the expiration of her previous deal with Wexford Youths.
Manager Hope Powell said, “It is great news that we have managed to bring Rianna to the club, as she is someone who will bolster our forward options.
“We have kept a close eye on her progress in Ireland, and I know she was very keen to come over to England and prove herself in the Women’s Super League.
“We are all very much looking forward to seeing how she progresses in the months ahead, and cannot wait to start working with her.”
Jarrett began her career with Wexford Youths in 2011, before she moved to the States to take up a scholarship with the University of Tennessese and play for the UT Martin Skyhawks.
She returned to Wexford in 2015 and has remained with the Irish side for the past five years. In both 2018 and 2019 she was also named the Women’s National League Player of the Season. She scored her first senior international goal in October during Ireland’s 3-2 win over Ukraine in a Euro 2021 qualifier.