I believe the skill increase is random -- there's a chance the skill will increase when the villager is successful. The chance is smaller as the villager's skill increases, so getting to master level takes much longer than reaching trainee or adept.

The hint you've mentioned will help her build faster -- and since she's building faster, she'll have more chances to gain skill. You can do the same thing with researchers and tech points.

You just have to be patient with this -- since the chance is random, it will happen faster for some villagers and slower for others.

Do not worry about training another builder -- your other builders can learn by fixing huts once you've finished all your building tasks anyway. (I have several master builders that were kids when I finished building anything -- they just fix huts all day!)