The time between your period and ovulation is typically what varies. However, the majority of us have about 14 days from ovulation to their next period. So, for example, if like me you have a shorter cycle of 25 days, you would normally ovulate around day 10 or 11 (counting from the 1st day of your last period), then get your next period 2 weeks later. That being said, it is certainly not carved in stone. You can suggest to your friend that she try ovulation predictor kits, that always worked best for me. You can buy them at the drugstore, or on line. Congrats to you on your pregnancy, and I wish your friend luck!
Mostly it is is day 12-16 depending on how long you cycle is. but you never know if or when you may be early or late, I would just tell her to use OPK's and congrats on your BFP