And this is what I like about ESTJs! I vaguely felt all of those things you said, EJCC, but could never have broken in down in such a succinct, easily understandable way. I'm so glad this thread exists.Firstly -- welcome to the forum!
Secondly -- I laughed when I read this post, because my mother is an INFJ and we have had similar issues to this. The issue is, that for ESTJs, there can be a fine line between blunt truth-telling and harsh accusation. We are direct and honest because it's for the good of other people and the work they do -- and we claim that we can take what we give -- but if we can't tell that the other person's motives are the same, and we can't tell that the other person still thinks highly of us despite everything, then we get defensive. We see the other person's comment as an attack, and an insult, and not as something constructive.
Some of this is inherent in ESTJ/INFJ relationships because of how Fi and Fe interact with one another; if something goes wrong, Fe-users like INFJs are more interested in accountability, making sure the other person knows what they did wrong and "don't do it again" -- whereas Fi-users like ESTJs are more interested in figuring out the thought process behind the incorrect action, so the thought process can be corrected. It's more process-oriented, than results-oriented. Which is why, when I've done something wrong, I've often had clashes after the fact, with my mom, because I'll try to explain myself (so she can correct my thought process), and she'll see it as making excuses, and will shut me down and just tell me to never make the same mistake. So, some of your ESTJ's defensiveness likely comes from situations like that, where she'd feel like you didn't care what you had to say, and were like a judge refusing to hear the defendant's evidence.
Generally, though, I would suggest that you emphasize the good, in the direct honesty you give her. Continue to be direct, but make sure she knows that you aren't judging her, and aren't trying to make her feel guilty. If she tries to explain herself, remember that she isn't making excuses, but is instead throwing out evidence for you to judge as valid or invalid. Acknowledging her intentions as being good, but telling her where her methodology was off, strikes a nice balance.