Look into the Tang dynasty. Empress Wu ruled on her own, and did not put her son in a puppet emperorship while she did.
I know that. I had thought that she initially came to power as an empress dowager, though -- declaring her own dynasty only after she had cemented her power.
In any case, I may go more for the route Cixi took than the Wu Zetian did. It takes someone very strong to go as far as to declare themself emperor, and I want this character to be not quite that strong (she's actually a bit of a puppet of the behind-the-scenes power).
Producer and Moderating Host, Conlangery Podcast