Not a GD, so here’s my 2 cents on the top 2 - build from scratch. It will be cheaper in the long run as you can have an upgrade path. Some SIs use proprietary parts that will screw you later. Any non-rolling distro will be good. If she is a long time Windows user, I would recommend making it have KDE for the desktop as it seems to be pretty Windows friendly in orientation.
A man of culture I see.