The simple answer is yes, you can choose the gender. There are many different methods and some are close to 100% accurate. Some clinics/institutes even offer guarantees that they will continue cycles of treatment until it's successful. The only drawbacks I can think of to note are (1) cost - but it can be covered, at least partially, by insurance & (2) multiples are more likely with some of the procedures.
Here's a link with 7 pages of good info.
I wish your friend best of luck!! I knew a woman that wanted a girl so badly that she had 7 sons before her body gave out on her (had to have a hysterectomy).
That said, I wouldn't leave it up to chance.
