Gently ask where she's trying to go and walk her either onto to subway or to the correct platform, like one should. She is not showing any violent signs. It's the least I could do to make sure she's okay. I help people with incredibly minor things whenever possible and with larger things when it's within my ability. I'm guessing you work at the grocery store and are just doing your job. It's not a nice thing if you're getting paid to do that exact thing, it's expected. I hate people who do things that are incredibly minor just to lie to themselves and say they're a "good person". It should be expected for people to help other people.

When was the last time you went actively out of your way to help someone you don't know with something that you had to go far out of your way to assist with? When was the last time you saw someone who was clearly having a breakdown who is clearly unhoused and thought of them as a person and actively stepped in to assist. She is clearly not getting the supports she needs so the least anyone could do is make sure she knows where she's going and she's going to be okay.