Hi
I'm an irelia main, but I'm a low elo scrub. But I have a good knowledge of Irelia.
One reason I m still in low elo, I do bad mistakes sometimes when I try to hard to carry and end up dying when I shouldnt have to.
Anyway.
As Shen, care for Irelia's level 1 cause she will outtrade you with her stun. But I 'm pretty sure you have a lead for level 2,3.
At level 4, any good irelia will take her W for true damage and will start to get advantage on you. There will be a point where irelia cannt kill you too much. So either you wait for a gank or you focus on farming and using your ult at 6.
Plus beware to not get all in as her Lvl 6 is defilenitely more dangerous than yours. If she gets to lvl 6 before you and you stayed close, you are dead.
As for Irelia power spike, her getting a Sheen ( trinity force ) is defenitely her power spike l. Dont even try to fight an irelia around 15 minutes its pointless. I can't count how many times i get gank top and end up getting a double kill.
Irelia + trinity is probably the biggest power spike in the game. Trinity is like THE ITEM MEANT FOR IRELIA.
Recently I'm always building a second dps item and it tends to help more .
So as versus shen versus irelia, i would either try to do a lot of dmg and zone her out during your level 2-3 or play passive farm and watch minimap to ult or TP
Just my 2 cents
and honestly I've won every single game and 2 out of 3 times I wreck her in lane. Still I feel like that only happens because the irelia I'm playing against is unskilled. Not bad, but certainly not an irelia main. So I want to know what her universal weaknesses are that I can capitalize on them in that matchup. When are her powerspikes? That sort of thing.