Early loss of one's mother
This story has a sad irony that underlies it. This journal is the journal of William Wordsworth's sister after the untimely death of their mother. The early loss of one's mother is ironic because it takes one of life's greatest assets—the support of a mother—and reverses it, making memories of her mother so difficult to bear that her grieving process is all over the place. Sometimes she finds herself able to think about her mother, but sometimes the pain is too much for her to face. The loss costs her her childhood innocence.
Instability and mourning
There is an ironic dilemma that faces Dorothy. Because she needs to mourn and heal, stability is of the utmost importance, and yet, stability is denied to her. She finds herself in a constant maelstrom of moving from place to place, newly orphaned. She doesn't really find any stability at all until she gets to stay with her brother, William. At the end of the journal, we see that he leaves her to start a new life with his young bride, and she starts the cycle over again.
Synchronicity in nature and poetry
When they are together, Dorothy notices that William's poetry is capturing something synchronous about nature. Their suffering is similar, which might be a hint as to why this happens, but still—it's perplexing how uncanny his poetry can be. It is as if he is reading from her intimate experiences of nature. Nature is synchronous with her suffering as well, in a sublime way, making her question whether they are truly alone in nature, or whether there might be a hidden being who draws near to them in nature.
Health as a battle
Instead of being mostly healthy with a few spells of sickness, Dorothy is mostly sick with a few moments of health. Her battle to be healthy is an additional layer to her suffering. The battle for health is paralleled with her battle for joy, and in both cases, she struggles to find the motivation and drive to push through the frustrating states that plague her. She must battle without the energy to do so.
The brother's departure
Her brother is her hero, and that's why it is such a bitter pill to swallow when he leaves her. Ironically, he leaves her to start a new family. He marries and leaves her behind in his move. The decision to separate himself from her makes her struggle again, because it seems that this new season is the one where independence will emerge, and Dorothy's depression and anxiety are going to be serious obstacles in that pursuit, as the end of the journal clearly suggests.
