Some people are of the school that the term 'she' should be used by default, switching from the traditional assumption that people are male. I personally prefer 'they' but some people seem to take offence/feel it's incorrect to do so. There's quite a tradition in CS writing where people being spoken about are female (can't think of any exact references off the top of my head though).
"Want to help someone out? She will probably use a Qwerty layout."
I'm not perfect and guilty as well mistakenly defaulting to a user on the internet as a male. Let's try to welcome both genders equally :)