Is your MC good at relationships in general?
No. Not really.
She had a very good, loving relationship with her mother. Her father died when she was very little, so her mom raised her on her own.
But her mom died when she was ten. And then four years bouncing around the foster system, mostly with pretty crappy foster families got her a bit jaded on relationships with others.
Her aunt and uncle took her in when she was fourteen. They were nice, but she never really got close to them.
When she got her dog when she was fifteen, that became the first relationship she'd really had since her mother's death.
A lot of the story is about her learning to build relationships with others, and overcoming her fear of getting close to people.