@AlexanderD -- is her Windows system occasionally doing something in the "background", e.g., a virus-scan, or "calling home" to download & install the latest Windows security updates? Such activity consumes some of her computer's resources, leaving less resources for her streaming app, causing it to slow down.
Also, check the Windows Event Viewer ("eventvwr" command on a Windows command-line prompt) to see if something is quietly wrong (such as I/O errors on the disk-drive) that cause multiple "events" per second to be recorded onto the disk-drive. Such "excessive" disk I/O can slow-down a computer. [ Been there, seen that. 😞 ]
