I think it is purely far-fetched to speculate which tiara will eventually go to whom. We actually strictly don't know.
The status of the jewels worn by junior members of the Royal family (occasional loan / permanent loan / gift in full property) is not always clear. The Cambridge Lover's Knot Tiara was worn by Diana, but it seems to have returned after her death to the Royal Collection, so Diana might not have owned it.
Personally, I hope that the Cambridge Lover's Knot Tiara (as well as other historic jewels having belonged to previous Queens) will remain in the Royal Collection, i.e. in the possession of the reigning King/Queen - which does not exclude them to be loaned to junior princesses of the Royal family.
Otherwise these jewels would eventually, after a few decades, not be seen anymore (because their owners will be too far from the "core" of the Royal family and will not take part to royal tiara-events), and will end up after two or three generations in an auction sale - as it was the case for most of the royal jewels given to Princess Mary, Countess of Harewood, or to Princess Marina, Duchess of Kent. I do not wish this fate to the lovely Cambridge Lover's Knot Tiara!
So I hope that all the jewels coming from Queen Mary, Queen(-Mother) Elizabeth or Queen Elizabeth II will remain in the Royal Collection, because of their historic and artistic value, and that Prince Harry's wife or Princess Charlotte will inherit (or be given) only jewels which had belonged in full property to Diana (e.g. her Saudi suite of sapphires and diamonds) or jewels specifically acquired for them (similarly, for instance, to the diamond tiara newly acquired by the Queen and presented as a wedding gift to Sarah, Duchess of York).