Hi,
From what I understand and have read, most definitely. There is always a chance that it will be either a boy or a girl. Certainly conditions make it more probable for a certain sex, but no conditions can rule out a sex. The conditions usually determine how quickly either the boys or girls can get to the sperm, but remember it takes thousands of sperm to break down the egg wall, so the first there doesn't even take the prize if you know what I mean. And with the timing of sex in a cycle, thats based on the sperm's survivals rate (females survive longer), so they recommend that if you want a boy to wait to when you specified because if the sperm are waiting for the egg the girls are most likely able to survive the wait. At the end I'of the day, there is always a chance, it may not be 50/50, but there is certainly a chance for either.
SO many other factors play a part, temperature, position, and I heard on the news a few months back new research shows one of the biggest contributors is actually mummy's diet.
I am certainly no expert, DH and I are wanting a son first of so hence the reading I have done. Hope it helps though.
Good luck for that girl! Who knows, if everything works out maybe our boy and your girl and meet up some time hehe jokes.