[Much of this source confuses Rosemary with her mother Millicent, but there is some more plausible and interesting material too. Although this source also makes the entirely unsupported claim that George V regularly drank to excess, it does promote the useful idea that the debauched lifestyle of Rosemary's uncle, James St Clair Erskine, 5th Earl of Rosslyn, would cast a scandalous shadow over Rosemary's proposed role as Princess of Wales.]
Aged 24 her pale blue eyes caught the attention of Edward, Prince of Wales. In her diary of Feb 1918, Lady Cynthia Asquith records, 'Edward dances with her, and motors with her in the day.'
Rosemary [is said to have] just smiled when the handsome young Prince first proposed to her. [But] she told her best friend, Lady Victoria Paget how, "Over six months she gradually came round to the idea of 'Queenship'". In 1968 Lady Paget's diary for 1918 was published by her family. The diary revealed Rosemary had told her, 'He's weak. Like a big child. But I think I can make something of him.'
Rosemary's father, the Duke of Sutherland, had left her a land-based-multi-million fortune. She was all set to make a perfect Princess of Wales. However, when Edward told his parents he wanted to get engaged. The answer had been a resounding NO!
Rosemary's 'larger than life' [maternal] uncle, the [5th] Earl of Rosslyn, was the fly in the ointment. The Earl was one of the world's big-time gamblers. He was celebrated for inspiring the song The Man Who Broke The Bank At Monte Carlo [though never managed to achieve that himself]. After being declared bankrupt, twice, the Earl had become a celebrity drunk.
[ ...]
The King and Queen Mary resolutely ruled-out any connection with the Sutherland family. Through no fault of her own, the lovely Rosemary wasn't given the opportunity to make something of the future King Edward VIII.