I wasn't saying Lash was providing the Hellfire on her own, I would say it was Lasciel footing the bill with the channel between her and Lash providing Harry access.
With the circle barrier around her coin, I'm doubtful Lash was able to get anything from Lashiel. And while it isn't strictly laid out, I suspect in most coin possessions, the shadow construct does have communication with the Fallen trapped in the coin, giving it access to the Fallen's Intellecteus.
However, by placing the coin in the circle, Harry circumvented this.
I mean, from Micheal's comments, you'd think that the coin would present an impossible to resist temptation. While Lash was tempting at times, she never really came across nearly as manipulative as Michael seems to suggest.
So that's my reasoning for Intellecteus being a factor.
...
That aside, the point remains, I don't see Lash being able to work directly with Lashiel, thanks to the circle. I think the only reason Harry might have been able to summon the coin from the circle is because it was his Will that created it.
If another Wizard had so confined the coin, that might not even be an issue.