Since she is 37, there really aren't many other good choices. As it is, she is high in the Down Syndrome and "elderly primapara" sweepstakes. And for a hereditary monarchy, adoption just isn't quite the same as for commoners.
I do hope that Kate and William have excellent security for their children.
FWIW, the Royals fascinate me. It doesn't seem to be a particularly easy or desirable life for those who are at or near the top. That's why Meghan's acting days might serve her well as far as being a Royal is concerned.