Each manufacture of router has their own means of QoS. Some you can control the protocol, application, IP or/and port. What is she doing that consumes all the bandwidth; streaming video, playing games, downloading music, video chat. QoS will give preference to all those instead of the PC doing web surfing because they are more resource intensive.
You'll need to play with your QoS to determine the best solution. You can also adjust her connection on her Laptop. If it's a LAN connection, then tell the NIC to only connect to 10Mbs instead of the 1Gbs. Depending on your router, you can create segregated WiFi Access Points and limit it's connection.