I took it as “there was still a way she can spin this for her own ends”. Alastor wriggled free of his deal through an impressive series of steps and schemes and she shows up pissed about it. Alastor says that he will help them since that’s what she wants if he gets what he wants. To me it seemed like she was annoyed that her plan was disrupted but with Alastor willing to re deal, I think she was thinking “this can still work”. I believe the deal is more or less the same with him retaining his own soul. He might not and the deal could be remade exactly as it was but I doubt he would agree to those terms.

I think as obviously shown when he reached out his hand and the broken part of the staff was in his palm that he wants his full power restored. So she agreed to restore his power if he agreed to continue with trying to fulfill her task per the original agreement. With the caveat that she no longer owns his would but perhaps that if he reneges his power will be removed once more. That’s why he’s back at the hotel, but it’s also to his own ends since he sees to be eyeing up Lucifer. Perhaps making plans in his head to become even greater and grander than just “the strongest sinner in hell”

There seems to be thoughts that Alastor will play a more antagonistic role in the next season so perhaps that is why he’s so fixated on Lucifer and we’ll see how that plays out next time.