Kindle 3 displays the entire '
Myanmar' code table (U+1000 - U+109F) but not '
Mayanmar Extended-A' (U+AA60 - U+AA7F). As to whether it is 'correct', I would not know. To the extent Burmese script requires use of ligatures, 'composed' characters, or special layout rules (as I believe it does), Kindle may not do that properly.
I was able to convert the Wikipedia article for 'Burmese' and send it to my Kindle (using a neat Chrome extension called 'Send to Kindle'). Most everything displays (except for the aforementioned Extended-A characters), but I have nothing to compare it to as my browser won't display Burmese. So again, I don't know if it is okay.
Getting the encoding correct is essential, of course. Unfortunately, I can't help you with Word's options - I don't use it often enough to know how to control the encoding it uses. You might try sending .rtf for the conversion - with luck that is UTF-8, which should work.
Another option is to create a PDF from the .doc. That will probably require either making the font size larger, or (better) the page size smaller, so that it is readable when zoomed to fit-to-page mode. It won't reflow, but at least the correct text layout should result.