Can I sync my friend's iPhone 3G to my iTunes so it can update, without wiping my music OR my friend's?

My friend needs the update, and we are overseas and I am the only one with a computer and an iTunes (and internet). If I plug her iPhone to my computer, what happens? I'm worried that my iTunes library will get messed up, or she'll lose EVERYTHING on her phone.

She said something about 'logging into her Apple ID' but I don't know if that's going to do anything?

How can we do this?

Thanks for your help.