MBP slowness... Causes?

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DP wrote:
What about the chance of malware

If, by "malware," you mean badly written, incompatible, or corrupt software then yes, I think you're on to something...

I say that the best thing for her to do is to save her own documents then do a nuke'n'pave. Re-install software, especially of the driver or 'helpful utility' kind, one-at-at-time and with great attention to the results.