Ellie's AI broke the game for me once.

I climbed up a ladder to get up something to check it out and she followed me. As I was looking around she sat down on the edge right by the ladder blocking my way. Then when I wanted to get off she wouldn't stand up and move and apparently you can't jump down so I was stuck. Only thing I could do was restart that section.

I've played it 11 times and never once found a situation where you could climb a ladder that didn't lead somewhere. Where exactly was this ladder you climbed? And I've also never seen Ellie sit down on the floor when I'm playing ... That must be an animation I've strangely overlooked in my 11 playthroughs.

I'd say your PS3 was at fault moreso than the game.

Count me among those who never experienced a single glitch or bug in the many playthroughs I did on both versions of the game.

I don't remember. Somewhere inside. Just before you get seperated, if I remember correctly, in some dark part (which may or may not be helpful depending on whether or not you get seperated more often; I never finished it). And well, I don't know what to say to your last sentence, it happened. I even tried to shoot her in the head but obviously that doesn't work. Maybe she just crouched, but I'm positive she can apparently sit down on ledges and edges.