Obviously, the author is paving the way for them to be together at some point. Yet another mismatched couple.
It's in the title, so all couple will be "unlikely", but will work.
It's in line with her afterword in her collection: she wants to write relationships between women that "work out", even if it's difficult. But not difficult because they are gay, but because they are human beings.
Explains the conspicuous absence of surrounding homophobia in her works. She's not writing about that.