Should Kate have thought about this from the start...

As if.

In any case, anyone who has dealt with Constantine's work can tell you what a dumbass he is, he's still a good magician. She needed help and he gave her the spell she needed. But Kate found out too late that it was the wrong spell and instead of what she needed, a demon stuck to her.

It would be more accurate to say that she has to hold you by the tail like a child so that you don’t run away to Gotham and create a real hell there. She doesn’t need more problems and now Kate has a headache when Constantine tries to explain to her how to remove the demon. But it's in vain.

You're torturing her, frankly speaking. Even now, when Kate opened her eyes in the middle of the night simply because she felt a weight on her stomach, she blinked before noticing a familiar face.

— "Why the hell are you sitting on me?"

It's not that Kate looks like a chair.