This part about her wanting to go to the 23rd century w/ Kirk always bugged me. Basically she tells Kirk "I've got nobody here!" (in 1986). It just seemed like an awkward, throwaway line to justify her wanting to go to the future w/ Kirk's crew. I mean, does she have any siblings, are her parents still alive, does she have any aunts or uncles (let alone still living distant relatives)?
shareIt's quite possible she really doesn't. I remember in the novelization, there is a mention of her father dying (He had Alzhimer's, and nobody from the Enterprise even knew what the disease was) -- it is possible that her mother had also passed, and she was the only child of two only children. If she had no close friends, having spent all her time studying and or working with whales, and no immediate family, she could literally have felt alone.
Her saying that didn't surprise me nearly as much as Kirk's superiors letting her stay. Of course the two or three times the Star Trek crew ended up in Earth's past, they happened to stumble across points or people that were pivotal in history. Gillian wasn't a pivotal person in history, like the astronaut that fathered a son that was vital to space development, or Edith Keeler.
Also, they really couldn't zap Gillian's memory... even if she agreed to never say anything, she would know that nothing she could do for her entire life would save her whales from extinction.
It's entirely possible that she was destined, that it was her future to come to the future and help current time understand whales.
How sad, that you were not born in my time, nor I, in yours.