Writing documents and using spreadsheets, creating presentations, reading and responding to e-mails, and browsing the web, which is what she uses, covers pretty much 99.999% of the uses a computer gets.

Do you have a concrete use case where Linux fails and Windows succeeds?

Whatever I tell you, you will have an excuse.

For instance, if I say I do something requiring an application for which there is no good OSS equivalent you'll tell me it isn't Linux's fault companies don't port their software to an OS with ludicrous levels of fragmentation that break compatibility nearly every release.

I have been in this argument many, many times over the past 2 decades. It is always the same. Deny there are problems, suggest insufficient alternatives, even recommend just changing their use case entirely. Anything to avoid saying "yeah, Linux actually isn't good for that".

Linux isn't good for making Windows users happy.

The 90s called and want their argument back. Also, slashdot says hi. :-)

Hmmm, mod 4 Insightful? or mod 2 Offtopic?