The previous reply is mixing two different Barbara Sinclairs.
The one being asked for did not marry Patrick Mowat of Balquholly. This is based on pure speculation done almost 200 years ago by a Norwegian author and can easily be disproved. Patrick married Margaret Cheyne and she was the mother of his eldest son Patrick. She was still living in 1548.
Andrew Mowat of Hugoland, whose mother Barbara is said to be, was born around 1535. He could not be the son of Patrick and Margaret as his coat of arms indicate a Sinclair ancestry, so it's most likely correct that his mother was a Sinclair.
It's however hard to find the parents of Barbara. Keep in mind she is not mentioned in any contemporary sources. Neither is her husband (called Bertel Mowat in old genealogies).