I was thinking that if you did say goodbye to Phyllis that the new mansion cage would be perfect for a BC. This is a nice looking boa, if you don't care about tracing locality for breeding reasons, then it's an amazing deal! I agree that her temprement may be a bit willy simply because there are no out of cage pics and the state of the cage but it's a boa and most can be calmed down over time anyways (but it could also be - fresh shed snake in a nice pose, so snapped pics, I've done that before). It would mostly come down to you - would you like raising a little one up and seeing how it turns out or jump right in to a nice adult and go from there.
Good luck with whatever you decide!