Honestly; Your REAL kitchen.
Get her some special things of her own that she can use in it (like a big bowl or two, and some bamboo spoons, and special towel for drying, etc.), and instead of her learning how to PRETEND to cook and help, she can actually learn.
18mo's can
- pour dry ingredients
- stir cold ones
- rip lettuce
- shake anything that needs shaking
- move chopped veggies from the cutting board to the pot/pan
- carry things from fridge or pantry to counter
- help wash dishes
- help sweep up messes
- throw things in the garbage
- etc. etc. etc.
Helps develop fine and gross motor skills, cognitive skills, verbal skills, color and shape recognition... and you train yourself up a HELPER in the process. As they get older, they can do more and more. They slow things down a little the first year, but by the 2nd they're speeding things up enormously. And you are teaching them MANY useful skills.
Kids this age are wired to copy adults (which is why play kitchens are a big hit with kids... they WANT to be copying and helping). When we give them tasks they can actually do, they keep doing them, and it's FUN.