Welcome to TG Rileah.

Web Designer 6 is now a very old version of the software in computer time I suggest you bite the bullet & purchase Webdesigner 365.

1: I would say you're running WD6. I'm not sure what profile you're referring to. Best log into xara.com & open your account to see what software you've purchased.

2: Simple answer would be no, both of you could use Xara Online via DropBox , google Drive etc. However the editing features in Xara Online are minimal and I have a feeling that a 50 page site would be difficult to co-operate on.

3: Yes you can, but you'd need to create the site first and then she could use Xara Online to amend it in a limited manner.

4: Xara doesn't have a native shopping cart, you'd need to use a widget like Ecwid. I don't know about zero fee carts.