Best way to be supportive of INFJ GF?

It's almost certain she doesn't want solutions but a listening ear and to know you are there for her - she probably needs emotional support, not practical or theoretical. If she's an INFJ she may want to fly a very high emotional kite into the abstract. It's not just an INTJ thing to be solution-oriented. I am very much that way myself and I have to fight it all the time - it's probably a male thing. This cartoon says it better than I can - I guess Dilbert is archetypal INTP and it's just so eloquent.

Try tapping into your inner Fi and give her as much of your inner concern for her as you can, but let her find her own path through the labyrinth of her feelings while you hold her hand.

 

Hug her. If it's cold, wrap a blanket around her. Kiss her forehead. And just listen. Empathize. Try not to solve it. Instead, walk with her through it. Talk it out as calmly as possible. Try not to inject opinion. Instead, help her navigate the polarities that she's juggling by riding it. Say, you hear her. Ask if there's anything you can do. If she doesn't say anything, have faith. Be patient.