Is there a way for females to continue gaining parenting skill after the age of 50?

I have a 53yo with 75% parenting skill...trying to get master. Have tried mating her and she goes to the hut, but no increase in skill.

If she went to the hut, there was an increase in skill, even if it wasn't apparent. You don't actually have to wait for the villagers to go to the hut. You can increase skills more rapidly by doing what's known as "speed kissing" to seasoned VV players. To read more about how villagers gain skills, in general, see this post.

You could try reading stories to the village children