onetapu: Partial success! My friend's gmail password was indeed wrong! She managed to change it (which involved driving 10 km to town to get her mobile to work!!) so we now know the user name and password are correct (finally).
We tried to email another book from Calibre but google emailed her back to advise they were preventing unauthorised access to her account and the email wasn't delivered. (So we know we have the correct user name and password at least).
Please please can someone talk me through exactly how to authorise Calibre in gmail settings. I have tried and can't figure out how to do it (simple steps, please!).
As an aside, I have recently set up another friend on wnation (through gmail) and it worked no problem.
I've just done a new calibre install and put in the default gmail settings and it worked right away so my guess is that your problems are at the gmail end of things rather than in calibre.
Perhaps you need to turn on access for "less secure" said in your gmail settings.