I have been growing, developing, through incalculable myriads of millenniums. All my previous selves have their voices, echoes, promptings within me. -- Jack London
I'm sure when many of us think of Ilia we are automatically reminded of Ocarina of Time's own farm girl, Malon. And it's easy to see why: they both live on a ranch, share an attraction for our favorite hero, care for Epona, and even share the horse's theme song.
Malon has a warm, cheerful disposition which seems to attract people and animals to her, beautiful character traits also be found in Ilia. Malon is partly responsible for the upkeep of Lon Lon Ranch and, being the sole woman of the household, takes care of her father respectively - cooking, cleaning, and housework. Living on a ranch, I assume Ilia shares most of the household responsibilities and loooks after her father. ...But being that her Bo is actually a hardworking man, unlike Talon, Ilia probably doesn't have to work as much or as hard as her predacessor. Malon seems to have little time for herself, but she takes it with a smile and remains thankful for her life all the same.
I often speculate Ilia could be a direct descendant of Malon since she assumes the role of the farm girl, even though they really look nothing alike. However, it should be noted that the Malon from Oracle of Seasons has rounded ears like Ilia.
Ilia not only takes on the roll of the sweet and loving farm girl, but also the one of a close childhood friend. Saria played this exact same part in Ocarina of Time, having been with Link from day one up and to his adventure. She and Link shared a special bond, one Mido was often jealous of, and even though destiny forced them on separate paths in life they never once stopped caring for eachother.
Saria was Link's closest friend. He trusted her implicitly and relied on her support when teased by the other Kokiri for being the only "boy without a fairy." Later, when Link returns to the Forest Meadow, he is saddened when he notices the vacant tree stump where Saria use to play her ocarina. It was obvious he missed her and his long lost childhood in the forest. Saria was a very loving and dedicated friend to Link and I think it says a lot that Nintendo would have Ilia replicate that same connection in Twilight Princess.
Ilia, like Saria, emparted Link with a musical charm; Saria gave to Link the fairy ocarina and Ilia gave Link the horse charm. The last time they both really see Link is when he departs via a bridge to Hyrule. Ilia even shares Sara's little flip of hair, except hers appears to one side of her face rather than both. I would argue that Link/Saria is one of the more plausible pairings in Ocarina of Time if it wasn't for the sole fact she will forever remain a child.