If she's not talking to him anymore, and hasn't for a couple years as you said, I'd say don't worry about it, and so long as she hasn't downloaded the photos and videos to her computer and purposefully saved them and is keeping them behind your back. Jealousy of your partner's past is pretty common, we're all guilty of it to one degree or another, but so long as the past stays in the past, there should be no problem.
She may have just forgotten about the emails, and never deleted them prior to you out of sheer laziness. I hardly ever delete my emails unless it's junk, and I'm sure many others are the same way. I wouldn't doubt it if I have emails with nude photos from 5+ years ago, between people I haven't talked to since then, and they're buried in thousands of other emails. I wouldn't worry about it too much.
If it does bother you that much, then just ask her about it. If she gets upset and puts up a fuss about deleting them, then she could be hiding something, but if she loves you and her past is just that, the past, she won't think twice about it. And don't accuse of her anything when you talk about it, such as still having feelings for her ex, because like I said, she could've just forgotten about them, so approach her calmly. How would you feel if you had emails from a girl that you knew years ago and have had no contact with since, and she started yelling at you about it? Getting upset about each other's pasts isn't productive. It's your present and future that's the most important.