In the title, love and vertigo are juxtaposed. Love sounds like it explains itself, because it's a word we use a lot, but the truth is that Grace spends the entire novel trying to sort through what parts of her mother were loving and which were selfish or unfair. This is important because the death of her mother has left her in desperate need of peace.
That leads us to vertigo. Vertigo is a state of severe disorientation that is commonly triggered by heights. A plane flight, for instance, might make someone severely disoriented, which is one thematic connection, since Grace has flown to so many places. The "dizziness" of vertigo is an apt metaphor for her suffering in life in general, since she feels that by moving around so much, she can't get an oriented sense of who she is and where she comes from.
Grace's freedom comes when she identifies with the part of herself that responds to change with adaptiveness and resilience. This ends up being a more significant part of who she is as a person than her citizenship to any nation, or her ethnicity, or even her family's expectations for her life. In other words, Grace is defined by having to be too many different people at once, and the result is that she sees the existential dilemma of life more clearly than her family.
Perhaps that will help Grace to forgive her mother and her aunts for their unfair expectations for who she should be and what she should accomplish in life, and how she should feel about her cultural identity. By forgiving her family, she can remain part of it in spirit, while still pursuing her fate independently.
