I'm surprised that no one has suggested it yet. But, FileBrowser is exactly what you're looking for! Set it up on your PC with docker and point it at any directory you want, put it behind a reverse proxy, make your daughter an account and you're done. It should work perfectly for you as it's designed to handle situations exactly like yours. Willing to help further if you need, dm me.

What about something like SyncThing that will keep one or more folders in sync between your machines? You'd end up having two copies everything (one on each machine), but it's super simple... kind of a 'set it and forget it' thing and you'd never have to worry about mounting shared drives, etc.

Windows nearby Sharing is what you search

The simpliest way I found to do this on Windows is HFS https://www.rejetto.com/hfs/?f=intro

You still need to figure out either VPN between your computers or port forwarding to make it work over network though

Edit: and sufficiently secure it if youre planning on running it online at all times

I don't understand all these complicated suggestions... just install an FTP/SFTP server and call it done. You can share your entire hard drive if you want and she can connect from any web browser (or she can use dedicated FTP client software like WinSCP or FileZilla). I have been running an FTP server to share files with friends since 1994.