Why do my bounces sound distorted on other computers?

Every time I send my bounces to my friend's computer they end up really distorted. They all sound good on my own but not her's. I've sent them through e-mail, gobbler, and finally just put them on a flash drive and transferred them manually. But they still sound the same every time, by they .wavs or .mp3s.

Any idea what's causing this? And, more importantly, how I can I fix it?

I'm using Logic Express 9 on a Macbook Pro (10.6.8).