My wife has suddenly started enjoying sex

We've (M: 38, F; 33) been together for over 10 years and have a 7 year old daughter that we adopted. Since the start of our marriage, my wife has never really enjoyed sex, although she has never ever rejected my advances and has always been available when I wanted her.

However, since the past week, she has been enjoying sex. She even let's me play with her vagina and enjoys it, which was never the case. I am trying to understand what might be going on, and what can I do to have this phase last longer :)