Welcome to the Watercolor Forum.
Your portrait is lovely, especially since you are using watercolors which aren't your primary medium!
I think your niece's hair and skin are lovely. You could probably darken the area around her face a little more, but overall I think you did great. I really like how you did her nose giving it form without outlining it!
As for painting landscapes, well my hand is raised beside yours saying "Me, too!" I do like to paint architectural subjects though, so any landscapes I do usually have a building in them.
I hope you'll keep your watercolors and keep practicing with them.