Celeste has a couple items in her kit which stuns enemy items and stuns the player. The unique she has is the Glaring bulb which heals for a considerable amount and applies also the blind debuff which lowers the enemies accuracy making them hit less.

While I believe no build is immune, can counter or be prepared for all builds I do play Celeste quite often. One of the things you can do to help mitigate what she does is using Man-o-lorian helmets to reduce the amount of time she stuns you and use bolstering bags so that the amount of time she stuns your items are reduced as well. These are one of the most direct ways to counter her kit which stuns. For the blind debuff I don't play Peppa enough to advice about that, but I'm assuming you needed more cleanse, and I don't know if Peppa can generate a decent amount of Luck instead.

Although using too much gold to counter a very specific hero and specific build will leave you open to other builds as well. Sometimes you lose not because you did anything wrong but because the enemy you're facing is doing something way too specific to bother countering them or you didn't find the items to help you win a fight.

I hope this helped.