Major Arcana 16: The Tower.
The tower represents change, someone who holds on to an old security or some idea, presence, person or material that will eventually lead to a fall. This is not necessarily bad, but it can be. Someone who clings to security, or what makes them feel safe—feel good—will eventually see their “tower” fall. In ways, this can be seen as a fall from grace. And it can be. When wisdom must be forced upon you, or ignorance must be taken away, the tower manifests itself.
In summation, The tower represents a person who is holding on to something that they need to let go of. It shows that this object or idea that the person is holding on to will lead to a falling. Something that was once there for you can no longer be there.
For Holly, I think it shows how she clings to the life she was used to. It’s hard for her to forget that she lived on the streets and the tragedies that led her to where she is today. She doesn’t believe that she is more than that, and refuses to believe that she can be more than that. Holly clings to Selina and believes she can be some kind of a savior to her. Holly depends on Selina to help her to stop thinking the way she does but of course, out of fear she would lose Selina, Holly doesn’t tell her any of the feelings she might be going through. She is dependent on Selina for things that Selina can’t provide. Holly falls back on to her comforts, and has trouble breaking out of her bad habits. Holly has built a tower, eventually, she will not be able to keep it up. The tower will fall. It must fall, in order for Holly to mature. Holly has matured a little, and certainly now views Selina as much more of a human figure.
Mara’s Awesome TL;DR (bolded the stuff to show the main points): Sometimes it’s important to remember that cheese has saturated fats