I would suggest considering not using a wireless router, and just using ethernet cables and a normal router.

Wireless is kinda shitty, but if she's set on wireless than just get an 802.11g router and an 802.11g adapter. The quality shouldn't vary much between products, but I prefer Linksys.

Most routers act as physical firewalls, such as Linksys, as for the USB key I would look for any other option than a USB wireless adapter, you'll pay for that choice with unreliable connections and poor download speeds. Get a PCI adapter.

So if performance isn't all that important than go with USB adapter and wireless router.

If you don't mind spending a bit more and not getting better performance then I would get a PCI adapter for the PC and and another adapter for the Laptop with a wireless router.

And if your only concern is performance go with wired.

And yeah all routers are going to be compatible with your ISP as long as you have a cable running into your house.