Ask HN: How do I help an employee to become a better web designer?

I have a junior web designer without much experience, that I want to help grow and become better.

Not so much the technical HTML/CSS/JS side of things, but creating beautiful designs that provide a great visual user experience, highlights what is important to the user, has pleasant color combinations, the right amount of whitespace etc.

I am an engineer at heart, and while I think I know good design when I see it, I am completely useless at figuring out how to help her get better at this part of her job.

She is the only web designer in a small engineering-focused company, so nobody to learn from internally.

How can I invest in her becoming a better designer? Online courses, books, something else?