My thought was that she did manage to talk to him, but she is not present in Fangorn during the events of LOTR and so we don't see her in the books.

Bunn's request was for First Age or Second Age. Even by Entish standards, that makes for a long time in which a lot could have happened to her. Or maybe she just wandered off somewhere! Or maybe she even found a place with her brother where both their hearts could rest and that wasn't in Valinor, after all!

I fear her path did not always run smooth!

But in my response to Lyra, I came up with an idea for a possible happy end...