I have to agree with most of the comments here to the effect that she is just being nasty to you. Reine is right that it might not be jealousy, but the wording of the insult was effective at upsetting you. Your appearance is not just fine, it's great.
I'd seriously suggest that you re-enable your facebook account (most are only deactivated, not genuinely deleted), if you still have the PM, report the abuse to FB, then block her. She doesn't have the right to limit your social interactions.
The most common way that people find others "out of the blue" on facebook is by uploading the contact list from email, such as yahoo or hotmail, and if she's your ex, it could even have been because she had your email address from before you separated. If you want to cut down on any possible problems with people you don't want contact with, make sure that no email address that they might have is connected to your facebook account. If necessary, create a new account on google, yahoo or wherever, add that account to your facebook account, then delete the existing email address.