You mentioned you only visited her once. I will guess it was while she was unconscious. On Mars did you respond to her by picking the bottom right dialogue?

The only way to have her say that line is by not talking to her in the hospital and treating her poorly on Mars.

In all honesty, even though I'm not a big fan of Ashley as a character, I always tried to treat all of my squadmates with respect and the highest integrity.  I don't recall what the dialogue options were, but in this playthrough I would have chosen whatever I thought the highest paragon option would be.

 

There was nothing funny about that scene. The pathetic so-called squadmates stood there like the idiots they are and not say anything while Udina accused Shepard of being with Cerberus. Had they spoken up, Ashley may of lowered her weapon.

That's a really good observation regarding the squadmates.  Although one of mine did speak up.  With her gun.  The scene was funny to me because I thought I was taking all of the necessary precautions to preserve squadmates through this run, then EDI just blows a hole in Ash, and then as I'm sitting at my PC mouth agape, wondering what just happened she delivers the line to add insult to injury.  A perfect storm of incredulity.

 

The other thing is depending at what dialogue option and using the interrupt, will determine if she is shot or not.

If you did talk to her poorly on Mars and you didn't talk to her in the hospital, you can avoid shooting her, but she will not join you on the Normandy.

Also if you are nice to her on Mars and talk with her in the hospital, she still can be shot  depending on what you do.

The only thing I can think of is that I didn't visit her in the hospital when she was conscious.  I missed out on Thane because of this too.   Note to self, visit Huerta multiple times.

What did you do? *interested*

Seriously, I was completely shocked by this.  It's only my 2nd playthrough of ME3 (first with DLC).  I'd spent some time with Ash in the ship prior to Ilos in ME1 (I wouldn't call it a "romance"), and otherwise chatted with her occasionally in a positive way.  Not giving her any special attention, but not being overtly rude.  My first playthrough, I resolved the situation peacefully and Ash joined up.  This time, POW right in the... abdomen.  It's a little weird, since the shot taken was by EDI.  You'd think she would want the death to be quick and efficient.  Makes you wonder about how much reaper code she has running through her.

Well, at least when you kill Kaidan he doesn't damn you to hellfire. OTOH, Ashley's response seems more realistic.

That's the funny thing, I didn't even kill her!  I was just standing there wondering why my options looked slightly different this time than the last time I played through, and EDI made an executive decision to end her.  So I'm there with Ash thinking "hurrr.. uhhh... medic.. durrr" and she delivers that bomb.  I almost went back and replayed the mission so I could shoot her myself.

Found out that only visiting Ashley in the hospital once will result in her desire for me to experience an eternal flaming damnation at the hands of those destroying the galaxy.  In other related news, resolved to save Kaiden next time.