How did her cat come to be trapped behind a door that doesn’t open normally? What more can we do to help?

The cat became trapped because this was trouble conducted by this wayward spirit seeing an opportunity to cause some mischief. We do not see his presence as being a great danger, but it will certainly be much better to have this energy removed once and for all, and will benefit him the most. Your doing a repeat session on his behalf will help speed up the process by doubling the intention for this to be a successful outreach. It will simply take more time to do the deep healing work needed here for the trust issue, and this will help open things up and allow him to explore what we are saying provisionally, and that will be the convincer. Once he starts to feel a love vibration, there will be no turning back. So we simply need to get to that point.