Also, people have mentioned her ATM activity as possible proof she wasn't relapsing.
We only know there wasn't activity late that night, correct?
Which means PH certainly *might* have had some cash on her person from other withdrawals, from paychecks, from anything, really. I'm assuming she had at least a few dollars to go out with? Even people who rely on plastic usually have some small cash.
Isn't heroin relatively inexpensive? And if FH had bad intent, it isn't so hard to imagine him being like "This one's on me."