her instead of "his or her"

Hello everybody,

I'm new here and I'm very glad that such a newsgroup exists. I'm not
native
english, but I like english language. I've written a do***ent in english
(it's a silly one to be honest, don't expect anything serious) and I'd
like
to know wether I made any mistakes in it. 
The do***ent is at

http://www.sulweb.org/lucio/index.php/Howto_Reading_Howto

Maybe I've made several mistakes in it, but I'd like to focus on a
particular sentence. A friend of mine pointed me out that in the following
sentence

"If someone decides to waste her time to translate this stuff..."

the word "her" is wrong or, at least, restricts the meaning to women. On
the
other hand I'm pretty sure that several articles on the net use "her" to
refer indifferently to men and women in similar sentences. Unfortunately I
have no examples at hand and searching for "her" with google gives a
little
too many results...

The other chance is that I've never understood the real meaning of many
articles around...

Where's the truth?