Which is just as well for Harry, as getting it right with Ragland is crucial to his future with Markle.
The reason for this lies not in the unique circumstances of the British Prince and his American actress sweetheart, but in the relationship most women have with their mothers - one best summed up by the words: "it's complicated".
Beneath all the complications, however, lies an ineffable bond.
Who else can you ring up, well into adulthood, to ask whether the chicken fillets you bought at the weekend will still be edible today? Who will tell you with brutal honesty when your new haircut just doesn't suit you? Who will love you unconditionally?
An overwhelming majority of women can answer: "my mother." Enter into this relationship a male suitor to the daughter, and tensions can quickly arise.
Ammanda Major, head of service quality and clinical practice at Relate, says: "The relationship daughters have with their mothers can be very intense and a man coming into that can feel like an outsider. Sometimes the woman is sharing an awful lot with her mother, including details of her sex life, and the man can end up feeling there are three people in the relationship."
To overcome this, she says, it's important for both parties - the man and the mother-in-law - to get a feel for who the other really is. "It's about listening to them," she explains.
"It's a relationship that needs careful attention from everyone involved."
Most mothers will be asking themselves the following questions: is this man good enough for my little girl? Will he be a good father to my future grandchildren? What are his values/career prospects/bank balance like?
Ragland, 60, who is said to dote upon her daughter (and the feeling is mutual), need not worry about the latter, at least. Like Carole Middleton before her, she can rest assured her daughter will be well looked after.
Unlike the Duke of Cambridge's mother-in-law, however, Ragland is African-American and got divorced from Markle's father, Thomas Markle, when Markle was a young child.
Her distant ancestors were slaves and her great-great-great-great grandfather had been put to work in the Georgia plantations.
He was emancipated in 1865 after Abraham Lincoln abolished slavery.
Permitted to choose a new surname to mark his freedom, he selected Wisdom - which Meghan wrote movingly about in an essay for Elle magazine calling it,"the choice he made to start anew. He drew his own box."
If the Middletons, as non-members of the aristocracy, were seen as outsiders, Ragland - a social worker and yoga instructor from Los Angeles - is even further from the British establishment.
Understanding a potential mother-in-law and making her feel included is important in any family, Major says. In Harry's case it will be all the more pressing.
Meanwhile a man's concerns about his mother-in-law are often simple, boiling down really to: a) Does she like me? And b) Will my girlfriend/wife turn into her one day?"
"For some mothers the man will never be good enough and that's really tough," says Major, a trained sex and relationship therapist. "It wouldn't matter what he did. The mother can fear the loss of her daughter because it can feed into feelings of abandonment and fears of having an empty nest."
In most cases, however, it will just be a case of rubbing along as best you can. "You don't have to like everyone tremendously for it to work. You just have to understand the boundaries and make it work so it's good enough," says Major.
"You don't have to love your mother-in-law but you do have to understand her position and realise that her motivation may just be that she wants the best for her daughter."
But for a man, it's not just about getting your wife's mother on side. As clinical psychologist Linda Blair points out, women often model themselves on their mother, consciously or otherwise, and take on the role they've seen their mother play. Therefore "not liking your mother-in-law is not liking your partner," she warns. "To be difficult with your mother-in-law is to indirectly criticise your partner."
So what about the other way round? Markle, who has already been married once, will not have a relationship with a mother-in-law to negotiate if she marries her Prince, given Harry's loss of his own mother, Princess Diana, in his childhood.
But for many, the tensions between a woman and her mother-in-law can be all too present. Thousands of conversations on the subject have taken place on Mumsnet, where the "MIL" crops up as a frequent source of frustration.
Complaints about this other woman in our lives range from the little niggles - MIL letting herself into the house with her spare key, or sharing her old-fashioned views on family life - to the jaw-dropping: "My MIL has offered me £7,500 to have an abortion!"
Those wishing to stay safe in the MIL minefield would do well to heed Blair's belief in the power of silence: "If you're upset by a comment your mother-in-law makes, don't answer. Just wait. Usually most things will blow over."
