If there is one thing I've learned about the Queen over the years, its that she is a woman that is not only dedicated to her role as monarch but she keeps on top of everything that is going on in regards to the monarchy. This includes all the items in her red boxes, her patronages and her "Firm". She loves to ask questions.
Its not surprising with the Queen and Philip well into their 90s that they realize that its time for the "team" to take over charities and patronages and they actively start thinking about who would be the best fit for that certain patronage. It was planned eons ago (well it seems that way in the royal world) that it would be Edward that inherits his dad's Duke of Edinburgh Award Scheme along with the title when it becomes available.
Meghan is fairly new to being included in the team but then again, when we think about it, William, Harry and Kate actually are relatively new to being full time working royals for the "Firm". That's pretty much empty dinner plates at the table to serve up new patronages for the "Firm". The Queen doesn't just "dish" out her patronages but carefully checks with her family as to who would enjoy it most, be the best fit and goes from there.
I love the analogy that, I believe it was Marg, gave that when it comes to the monarchy, the Queen is gracefully gliding along in the pond like a beautiful swan but underneath the water, those swan feet are paddling fast. The "Firm" is always in motion.
Most likely Meghan will start out with a short list of about 4-5 patronages and in the first months of 2019, will officially visit them. She probably will keep active with her work during her maternity leave too but just not out and about in the public eye but rather doing behind the scenes work learning, planning and plotting for what is to come. Even into the fall months for when she returns to full time duties. She won't be idle.