So she has like 3 computers total? Make the laptops wireless and the desktop wired since the router's going to somewhere nearby the PC anyways.
You need to make sure the wireless laptops have wireless adapters installed or newer laptops tend to have build in wireless capablility (yeah, baby). If it does, there's nothing to worry about in regards to the laptop. If not, then you will need to purchase two additional wireless cards for laptops.
This is a really nice wireless one for notebooks. I love the built in attenna although pricey:
LINKSYS WPC54GX IEEE 802.11b/g 32-bit Cardbus Wireless Adapter up to 54Mbps Data Rates Up to 128-Bit WEP, AES, TKIP, 802.1x - Retail
For the PC, on the back of it there should be an RJ-45 port (fat telephone plug as I like to call it) where you can plug in a CAT5e cable to the router. Here's a link for a Linksys wireless router. I have the same model and works like a charm:
LINKSYS WRT54G IEEE 802.11b/g, 802.3 Wireless-G Broadband Router - Retail
Follow the Linksys instructions. THey make this really easy to read step by step instructions on what you need to go to get internet sharing. After all that, you can setup MAC and IP filtering or encryption if you wish using the router features.
Then if your "client" want to share files and printer, just enable it in Windows on each PC connected to the network.