The URL you provided is not the login URL you would be using yourself.
From a quick look it looks like a white label solution for schools, which host
their version of it respectively run their own education programs on it.

Let's focus on your main objective, which is
- videos
- quizzes
- documents

I think you make your life easier, when you download the data manually one by
one. 

Videos:
search for browser plugins to download videos (Firefox + plugins may seem
often a good combination).
Videos you then play with whatever (default) player your computer comes with.

Documents: 
as you wrote "documents", I assume these can be anyway simply downloaded. So
just download them.

Quizzes:
according to your description they may seem a) JavaScript-based, and (most
likely) b) require backend ops. This is anyway not possible to copy, not for
HTTrack nor for any other tool.
Just make the quizzes with the system and take screenshots - before and
afterwards. Then you can preserve the information for repeated learning of
your daughter.

Since the amount would only be the material necessary for your daughter, the
data to handle via manual downloads will be very manageable and you should not
bother with any technical tools and "internet details".