LL expect a blow to the gut from your D in response to your txt. not because you were wrong, you werent. but because it may become a dominance thing, or "hand" as Seinfeld called it. She'll want to recapture the upper hand that you took by telling her she was out of line.
if it does happen, then stick with your assertiveness and while you dont want to attack, dont back down.
have you ever read The Fountainhead or Atlas Shrugged? both these books deal with personal boundaries, and not backing down from your beliefs. i've found them to be motivating.
"In a ham and eggs breakfast, the hen is involved, but the pig is committed".