The little killer whale came over.
Luke didn't have a good solution for this newly orphaned baby. It was already good enough that he didn't let Selina eat it.
Nature was cruel. Other animals wouldn't let you go just because you were cute.
Of course, what human beings loved to do most was tamper with nature.
Since Luke and Selina were free, they simply left with the little fatty to look for other killer whales.
Killer whales could hear the calls of their own kind from a distance in the water. After listening for an hour, the fatty finally found a pack with just two big killer whales and a small one.
Luke used Mental Communication + Mental Hypnosis + Illusion to create close feelings between the little fatty and the new killer whale family.
Lone killer whales would join other killer whale packs to begin with; Luke was just reducing the friction between the little fatty and this new family.
Also, the little fatty was a girl.