She's using BarryM Instant Nail Effect polish.
How to create this effect?
Step 1: You need to put on a base coat (let this dry)
Step 2: Apply a light colored nail polish (let this dry)
Step 3: Apply the crackle nail polish and see the effect (let this dry)
Step 4: Apply a top coat (let this dry)
There are also crackle top coats available of the brand P2.
What do you girls think about this nail polish trend :) ?