It isn't always going to be a 50/50 chance. You would think it would go back and forth between heads and tails every time, but it doesn't because there is a 50% chance it could land on the same side again.
You'd say that although that seems correct, since there's a 50/50 chance of each outcome, it doesn't necessarily guarantee that it will ALWAYS be 50/50. However, her guess has the highest probability of occurring, or in other words, its more likely that it'll be somewhere close to 240 rather than in the 100's or 300's.