Every modern dictionary disagree. English usage of singular they dates back to 15th century still you assert it here without any argument. Nothing wrong with asserting things if you do that with stuff disprovable by one dictionary/wikipedia search though you make not too bright impression to put it mildly.

As to using she it's very common convention these days in some domains. Many books on games use that for example (chess, bridge, go, poker - you need to a pronoun for black/white/last to act player there ). I also saw some computer science books using it. At this point I would say it's so common that it becomes part of the language. I personally like it although I can see how it raises eyebrows when encountered for the first time :)