It was never stated that she has mastered all three types of Haki, just that she is one of the very few people being able to use all three types of Haki.

These are all the confirmed users of Haoshoku Haki so far. So she is one of the 13 people currently confirmed and alive to have it. The other two types of Haki can be learned by literally anyone, most pirates in the new world can use them.

It was also confirmed that all vice admirals and above of the marine can use both types of Haki.