I would not rely on Open Office for OS X. I found it to be counter-intuitive for anbody who isn't an X-windows geek, and I am an X-windows geek. It's just not as slick as the Windows version of Open Office.

There is some Open Office-fork that puts a real Mac windowing interface around it, but the name escapes me at the moment.

If I were Peg and it were doable, I'd probably just buy the real MS Word or MS Office. Otherwise she'll spend some amount of time fiddling as opposed to Just Writing.