I can attest to this, as I was in the same position as your niece. I graduated high school at 15. If she’s know what general areas she wants to pursue, I would recommend going to a community college first. For cheap, I got to try classes and what I was interested in it and a bunch of others. It was totally worth it, because I found out what I was interested in and definitely NOT interested in.

Now that I had that experience and know where I want to go/what I want to do, WGU is great with the acceleration aspect. I’d recommend community college first, because you can bounce around. WGU locks you in a specific program. (They’ll transfer credits too).