legal, of course
ethical. well being super strict, no.. business email SHOULD be for business only... but it rarely is. it would be nice to get a free gmail account just for correspondence, esp. if she gets a lot of homeowners related email..
but in reality there is nothing wrong with it, and i'm not really sure why everyone is upset? the only one who might have an issue with it is her employment, and not the homeowners.. she probably feels that this is the quickest way to get in touch with her, and emails to any other account would go unanswered or take days and days to get to. (most people constantly check their company email)