From the little I know about the British royals receiving gifts, what I do know is that each and every gift received is cataloged and acknowledged. What will happen to a gift sent to Baby Sussex, I don't know but most likely your friend will receive a "thank you" note acknowledging the gift. It may not be directly from the Duke and Duchess of Sussex themselves but from a member of their staff stating "The Duke and Duchess of Sussex appreciate..... " That sort of thing.
No law can be sacred to me but that of my nature. Good and bad are but names very readily transferable to that or this; the only right is what is after my constitution, the only wrong what is against it.
~~~Ralph Waldo Emerson~~~