The only reason I'd suggest she pass judgment now is if they find that Cassie's medical problems are a result from her response to the stress and change in her lifestyle, which can impact anyone's immune system and ability to fight illness, etc. Otherwise it definitely would take some time to decide, especially since the new cat might grow out of some of his playfulness in the next months which might be just what Cassie needs. I wouldn't make any decisions for a few months, but after that I think they just get stuck in their patterns and things wouldn't change especially if all integration efforts have been problematic.