"For starters, she's my niece"
Why does Tom say to the radio DJ that Allie is his niece? Later on, the DJ asks Tom "how's your niece?"
We know that Allie is Tom's half-brother's daughter's daughter (Tom -> Jacob -> Lisa -> Allie).
To be pedantic this means, Allie is Tom's half-brother's granddaughter.
Another way to describe the relationship is that Allie is Tom's half-niece's daughter (Tom -> Lisa -> Allie).