ciężko myślący in English:

She's rather clueless.

It's unlikely she's as clueless as you think.

My mom is clueless about my drinking on weekends.

Most ​people are ​completely clueless about ​tide ​directions and ​weather ​conditions.

He tried to fix the engine, but he is completely clueless about car repairs.

I can't believe you're so clueless. You're like a babe in the woods.