Sounds like someone's never been in love. It doesn't matter the situation, love is love. You can still be in love with someone that you know you can never be with. Sometimes it makes that love even stronger. Otherwise, I agree with what you said.
Sweetie, I'm one of the oldest forum members here and am well aware of what love is. My relationship is almost as old as some of the users here, and I'm sure my grasp on the concept is a little more developed than many of the younger members' here....
ANYWAY...
What I was trying to say is that had Saria understood the circumstances, meaning, had she understood that he'd grow up to be a man while she retained the mind and body of a little girl, she probably wouldn't have even become involved with those feelings. "Love is Love" doesn't apply to all cases (especially in cases involving very young people), and a person like Saria can hardly comprehend the magnitude of the term "love" in its true romantic form. All she'd be able to do is feel puppy love, the kinds kids do, which is nothing at all like something a real mature couple would feel.
If she was able to understanding that (which she'd probably never be able to, having the mind and body of a child and all...) she could never fulfill that role, she'd probably have been the typical kid thing and go for somebody else who'd be interested in her... like Mido who, despite being a bully towards Link, seemed perfectly capable of showing a softer side to Saria. I'm sure she'd still have treasured the best friend role, but I can't see somebody like her keeping a puppy-love interest in somebody who could never return those feelings. Really, I can't see her keeping a puppy-love interest in anybody for a long time being that she just a little girl.
And, if you want to get even more detailed, she would probably have been frightened away from any sort of romantic relationship had she known of the future. She's Link's best friend, yes, but she knows him as a Kokiri. Just think of how alarming it would be for her to see her best friend in such an alien form- a form she could not ever share and one she never saw before. She's a smart young Kokiri and a fitting role for a sage, but she isn't as wise and/or as somebody as Sheik/Zelda. She wouldn't be able to even bring herself to fathom a relationship with Link had she known what the future held. In her eyes, she just knew she liked her best friend. She didn't know he'd become a man, and had she known, she'd probably have been scared away from any sort of puppy-love interest she had in him.
TL;DR VERSION
She couldn't handle it or even comprehend it.