a) If your friend has a modern version of Word, it should open the Word document you are sending her. (I am assuming that Hotmail allows file attachments, and provides a means of downloading them. I have never used Hotmail and have a very very low opinion of them for unrelated reasons). Word is cross-platform
b) If your friend has a not-so-modern version of Word, or virtually ANY other word processor known to Mac-dom, it should be able to translate a Word document you send her if you use the Save As feature and save it as a very old version of Word, say, for example, Word version 4.0 for Macintosh. All modern PC versions of Word can do that, I’m pretty sure.
c) If your friend doesn’t HAVE A WORD PROCESSOR, or has an extremely primitive one that can’t translate any version of Word whatsoever, you can print to PDF (assuming you have Adobe Acrobat or a freeware/shareware mechanism like GhostScript that will let you print to PDF) and email her the PDF, or even put it up on your web site and send her the link. Of course, if she doesn’t have a friggin’ word processor, she may not have Acrobat Reader either.
d) You can, as you suggest, send it as RTF, but if her word processor can’t interpret a Word 4 document it may also be unable to interpret an RTF document.
e) You could copy the document’s contents and paste it into the email message itself. She may end up viewing it without formatting, as plain text, but she would at least be guaranteed to receive it.
If your Word document contains pasted graphics, stick with options a or c, as other options may lose the images. If your document contains tables, avoid only option e, the others will preserve tables even if they lose graphics. If your document contains no formatting other than bold, italic, centered versus noncentered text, indented tabs, etc, you might give serious consideraton to option e, unless she needs to see it as you see it, aesthetically. If she needs to see it as you see it, use option c, even in preference to option a, as nothing is as WYSISYG as a PDF file.