Daddy-Long-Legs on stage just last year . . .

John Caird
Wikipedia

Jean Webster's epistolary novel Daddy-Long-Legs has seen stage and film versions, most recently by the director John Caird onstage in New York City just last year, as witnessed by Alexis Soloski, "Review: In 'Daddy Long Legs,' an Orphan With a Mysterious Benefactor," New York Times (September 29th, 2015):

The story begins as Jerusha Abbott, the eldest orphan at her New England asylum, receives the news that a trustee who calls himself John Smith has agreed to fund her college education. This John Smith demands that she send him a letter once a month, letters that he will never answer . . . . Because she has had one small glimpse of him (from behind and in poor light) and knows him to be tall - and further imagines him old and gray - she calls him Daddy Long Legs . . . . [His] actual name is Jervis Pendleton, [he] isn't so geriatric after all and . . . the affable impertinence of her letters has made him fall in love. Soon he is contriving to meet her, without ever admitting his philanthropy, and taking a more active role in steering the course of her life . . . . To watch Jerusha awaken to love and literature is a great treat . . . . Seen through modern eyes, the story does have its creepy undertones, though . . . [it] avoids the merest hint of sexual suggestion, which does a lot to de-sleaze the relationship . . . . But it's still unethical that Jervis woos Jerusha without disclosing his identity and at least a little disconcerting that this protofeminist tale ends with its plucky heroine rewarded with marriage to the man who has manipulated her for the past five years. Maybe she should write a letter of complaint.

Hear! Hear! An excellent summary! Fits the book, too!