When asking about a major issue or problem within a text, one can define this is two very different ways. First, the question may be referring to any conflict which arises in the text. Second, one may be concerned with any personal problems a reader has with the text (regarding Reader-Response Criticism). Given that the question does not directly state which one needs addressing, this answer will address both.
First, Jennifer Holm's Penny From Heaven possesses both internal and external conflict. The narrator, Penny Falucci, struggles with the death of her father. No one will tell Penny anything about her father's death, and she was too young to remember anything which may have been said. Penny also faces external conflict. Her fatehr's family is Italian-American. They have very strong feelings and emotions when it comes to certain things. Penny does not wish her mother to remarry, and her father's family is also upset about the possibility of this happening.
As for any personal problems or issues with the text, I do not really find that I have any. That said, some readers may shy away from the very straightforward nature of the author. Holm's does not try to mask the family's problems at all. Instead, she offers them up to the reader with great openness and realism. This may make some readers uncomfortable given the stark realism used in the text.