The payment is due Friday. And the conversation was last Monday. I don't really need her to pay her half before it's due, so I can wait. But how long? (BTW I hadn't read all the posts above so I didn't realize you had already responded, Wonka. :-) )
Here's a suggested solution:
Pay the entire bill yourself (if able to do so) and then contact W later asking for her portion.
The important thing is that we don't want W to associate opening up to you emotionally and being vulnerable with the knowledge that she'll get slammed with $$ requests right after. That would shut down W fast!