She has a couple of options to connect - some wired, some wireless - with various equipment options.
Conventional modem:
Run a phone extension cable under the door & across the room to where she wants to sit while dialling in conventionally, or
Setup an el-cheapo 2nd hand desktop PC (with a modem in it) next to the phone jack to handle the modem duties + a wifi connection built or plugged in to it and a second WiFi device for the laptop
This PC is left permanently on & uses Windoze or Linux to dial out on demand. It also manages the WiFi network connection.
ADSL
Optimum option: The ADSL modem has an RJ11 socket. Plug it into any WiFi router. It connects to the laptop's wifi hardware.
Note: Some wifi routers are available with a built in ADSL modem which makes a one-box solution to the ADSL+router combination above.
Not so optimum: The current ADSL modem she has only has a USB connection. In this case you'll need a PC with a USB port + a Wifi card in it to do the WiFi network stuff similarly to the modem + PC I mentioned earlier.
WRT to 802.11b or g or n for the WiFi network: 11b is quite fast enough for internet work. It operates at 11Mbs while broadband internet connections are typically 512Kbs up to 1 or 2 Mbs.
If she will want to watch video eg with a home digital entertainment system using her WiFi network then .g or faster would be more appropriate.
NOTE: If a desktop PC is part of the solution then it's essential to have it running a firewall. There's stacks of Linux out-of-the-box firewall setups. The biggest hardware hurdle is if the PC uses a Winmodem device to dial out ie non-broadband option. Some are supported under Linux whilst others are more problematic.