Fictional relative's tuna-salad-and-cracker-eating bird (4,5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

*(tuna) [anag: salad ] + POLLY ("cracker eating bird") "Polly wants a cracker" is a common phrase in English, which has appeared in the novel Treasure Island and in a Nirvana song of the same name, although its actual origin is unknown, and Aunt Polly was Tom Sawyer's guardian in Mark Twain's novel.