In an open letter in The Mail on Sunday, Tiina Jauhiainen pleads with the Monarch to use 'whatever influence' she has with her long-term horse-racing friend Sheikh Mohammed al-Maktoum, who is accused of holding his daughter captive.
Princess Latifa has not been seen in public since 2018 when she was drugged and forced back to Dubai following a failed escape bid with Tiina.
We recently released disturbing footage of the 35-year-old royal in which she said she was being kept in solitary confinement inside a 'villa-jail' and feared for her life.
Her friends have had no contact with her since last summer. The case has echoes of that of her older sister Shamsa, who was abducted from Cambridge in 2000 when she was 18 and has not been seen since.
In her letter, Tiina writes: 'I am humbly calling upon you to use whatever influence you have with your friend, Sheikh Mohammed, to persuade him to grant Latifa and her older sister Shamsa their wish for freedom or, at least, to supply proof they are still alive.
'Your country has a proud record on human rights and of holding people, however rich and powerful, to account for their actions.
'Given you so obviously value justice, freedom and family and that you command universal respect, I truly believe your intervention could help bring the ordeal of these two women to an end.'
The Dubai ruler has a vast UK asset portfolio, including a £75million Surrey retreat, a Suffolk mansion and a 63,000-acre Highland estate.
He also founded the Godolphin stables in Newmarket and it is his passion for racing that connects him to the Queen. The pair have been pictured together numerous times at the Royal Windsor Horse Show and at Ascot.
It was, however, reported last year that the Queen will now decline to be photographed with Sheikh Mohammed following a High Court ruling that found him responsible for the abduction of his two daughters as well as a campaign of intimidation against his youngest wife Princess Haya.
In a further bid to apply pressure on the Sheikh to release the princesses, campaigners want Foreign Secretary Dominic Raab to apply financial sanctions on his UK holdings.