I'm literally at a loss here, every time I play against irelia I end up losing once she trinity force. Even when I'm ahead she always comes back. The true damage + heal + initiate and stun is killing me. How do higher tier players deal with this?
trinity is like her biggest spike in the entire game
try not to fight her when she first gets it, her damage will start dropping off after she finishes her second item if she isn't building more offense
Well, a decent Irelia player will make sure their damage doesn't fall off. Look at Gbay99, he plays Irelia A LOT and his damage doesn't seem to fall off. Same with Ireliacarriesu. My advice to you is when she gets TF (Trinity Force) Take extreme caution when trying to kill her, Try to keep your HP above hers. Another tip, I'm sure you're aware of, her Q resets on a kill, One little strategy is she'll Q>E and then W til you're dead. I'm not ranked but I have played a lot of Irelia and I know how she works for the most part. I hope this helps.
Really, the only thing you can do is either, find an early game monster, and stop her before her power spike, or find a late game monster and fight her when she falls off. Unfortunately, Irelia needs a bit of work. Not matter how hard she feeds, she'll still be scary mid game almost no matter what you do. Even Gbay99, someone who mains Irelia complains, about this. So I would just pick a late game champ and just wait till she falls off.
Step 1. Pick 
Step 2. Wither whenever she activates Hiten style and give her a couple good whacks with the cane.
Step 3. Profit. EZ LANE EZ LIFE
Buy 
or 
if you're a tank. She has to stay in proximity to deal damage to you and melee you. So as reduction is great for lowering her overall dps. Cape allows for good sustained damage against her. Stacking hp would be advised.
Just make sure you keep up your farm and don't allow her to get a kill on you.
I have a relatively easy time playing against her with zac.
