I really love this book.
In symbolic terms (as opposed to more practical terms), the chapter when Rachel acquires the grizzly makes it pretty clear why she sticks with that morph:
I reached a trembling human hand down to touch the rough coat of the grizzly bear. His
nearsighted eyes watched me. I was nothing to him. I could not hurt him. He could destroy
me without bothering even to wake up fully.
He was beyond fear. Beyond doubt. Beyond pain.
"It must be nice," I whispered to him.
I touched him and felt his power flow into me. And yet, as I absorbed his DNA and imagined
myself becoming this fearless creature, I still could not forget the look in my father's eyes, or
the quaver in his voice saying, "But, gee, Rachel, I think it could be okay, you know?"
I could already feel the emptiness his moving would leave in my life. He could say he'd come
back every other week. He could say we'd still see each other just as much. But I knew it
wouldn't be that way.
I could imagine him packing up to go.
I could remember the screams in the Yeerk pool.
I could remember Tobias trying to joke about college.
Too much. Things that were small and personal, and things that were huge, all swirled
together in my head. Nothing made sense. It was too much stuff. Too much fear and guilt and
loneliness. Too many decisions. Too much.
You know, there are days when I just don't feel brave and fearless. There are days when I just
want to go to a ball game with my dad and eat popcorn and tune out everything else that's
going on. Be a normal kid.
But that wasn't the life I had. Not anymore.
It's sort of like in book 1 when Tobias talks about the depressed hawk he'd acquired, who had broken his wing and been trapped in a cage, and Tobias wished the bird could be free.