On her second and third spells, she was released both times because the sons in question had died quite young.
BTW, I was reading Dulcie M. Ashdown's 'Tudor Cousins' and she brings up an important question - why was Lady Lennox excluded from the will of her uncle Henry VIII?
Henry made this will in 1546, though he might have also made one in 1544, when the Act of Succession was passed. If he had no problem leaving his Catholic daughter Mary as one of his heirs, why not his Catholic niece Margaret?
Technically, she had a better claim to the throne than her niece Mary, Queen of Scots, though Mary was in the senior line - when Margaret Tudor had married James IV she gave up her succession rights. Lady Lennox had even been born in England. And, most importantly, she was the only member of the younger generation who had a son - Lord Darnley was born in 1545. So why did Henry exclude her? This is perplexing!
Apparently, she and Henry had an argument before he died, but he was not the sort of man to let personal feelings dictate the future of his dynasty.
Any theories?