Apology? Seemed alright, more to appease just to make her not get any more upset. The rest seems to be overacted or playing into an overreaction. If you explained everything, as explained here, I'd think anyone would realize that it was, well like I said, a misunderstanding. You weren't bothered by her sexuality and didn't mean to ignore the spouse, you also just didn't want to get a spiel on it (as you didn't really care). Using gay instead of lesbian or homosexual or w.e. can be dealt with by apology and something about didn't realize how it could be taken etc. etc. (or something to that effect). Seems an honest mistake considering how often same sex marriage and gay marriage are interchanged.
Don't get why she has to be an assistant coach, considering it's established enough she'd complain if her child didn't get fair playing time. Also sets a bad president of "complain to get coaching jobs (even if they are voluntary)." Plus, if her worry is her child being discriminated against by other parents, isn't that going to be more likely now she is assistant coach then before? *shrugs*
Get the feeling she went into the original situation believing (rightly or wrongly) that people/society will be unwelcoming because of her sexual orientation. So all your actions got viewed through that, and thus looked more malicious then intended to be.