I recently picked up Irelia and while she's a lot of fun, I'm having trouble winning games with her. I usually do ok in lane and end up with a positive KD ratio, but even when I crush my laning opponent, we always seem to lose the game. It would be easy to chalk this up to a string of bad luck or the other lanes just failing, but I'd rather assume I'm making some sort of mistake since that means it may be in my power to fix it and start doing better.
I've more or less been following this guide, and it seems to work fine (I usually follow a guide while learning a champion and start experimenting with their build once I have their basics down). The philosopher's stone takes care of whatever minor mana problems Irelia has early, the heart of gold gives her some early tankiness, and then once I finish her Triforce it becomes pretty easy to kill squishies, building full tank from there. My problem is, I'll dive into a teamfight after the initiation and kill one of their squishies, but then by the time I'm done they've already killed our AP and AD carries. Best-case scenario has me getting one or two more squishies for cleanup, but then we get aced and the remaining enemies take a few turrets. It's like, I can almost certainly kill whichever squishy target I want but it just takes forever.
So, what can I do to improve my Irelia game?