I've heard that Kate was not really able to help Meghan out as much as she might have, which is understandable with her own two young children and being pregnant and then giving birth several weeks before H&M's wedding. And, in any case, I'm not sure how much effort you are imagining Kate needed to provide in the first place. Meghan had plenty of help from her husband, royal staff, Prince Charles (who selected many of the hymns and music selections, suggested the Kingdom Choir, and also suggested including the Coptic Church minister for one of the prayer readings).... how lovely it was for Kate to put in the effort she did to help make Meghan’s wedding so special.
In addition, Meghan consulted with a wedding expert and she was directly involved in requesting the brilliant, young violinist, Sheku Kanneh-Mason's services (as suggested by Harry). Meghan chose her own flower arranger and cake maker based on her previous knowledge of them. Unfortunately, the Archbishop of Canterbury in well-meaning fashion selected the sweet and loving, but over-performing Bishop Curry, who didn't know Meghan or Harry beforehand. I really preferred the short, but more on-point to the occasion address given by the St. George's Chapel minister at Eugenie's wedding, along with the reading by a black minister whom Eugenie and Jack appeared to intimately know.
It's not as if Meghan was born yesterday. She was previously married. She had her own lifestyle blog. She was a busy actor on a long-running television series, while also taking advantage of other opportunities, including filming two Hallmark movies, creating two capsule fashion collections for Reitmans, doing modeling gigs, articles, interviews, and humanitarian work, etc., not to mention that Meghan had done a lot of planning and assisting on her friend, Lindsay Roth's wedding, in June 2016, as she served as chief bridesmaid. As well, the transatlantic romance took a lot of energy, commitment and planning, what with juggling a busy television filming schedule and different time zones, as H&M discussed in their engagement interview.