Task manager and/or Resource Manager should show you where your bottlenecks lie, but sounds like either disk (spinner vs ssd), memory, or cpu is getting pegged. This should show you what processes are using said cpu/memory/io, either kill them, or feed them more hardware resources. The sysinternals tools like process explorer and such are also helpful in seeing applications and/or system processes freaking out, including more hidden ones.
If still a spinner disk, the best thing you could do is get her any SSD to run the OS and primary apps on alone.
Could be windoze is just trashed after a while with applications coming and going, upgrading, breaking stuff, etc. Might be worth trying a clean restore of the system and/or wiping the disks with zero's to reset state ala fragmentation or if ssd, needing a reset with secure erase.
-mb