This sounds a lot like:
The Once and Future Taiyoukai by RosieB
Summary: The well was supposed to be stable. It was supposed to send her to Inuyasha. And it failed. Now, Kagome's even farther into the past and she must depend on a young Sesshoumaru, who has no idea of what their shared future holds. But neither does Kagome.
Rated: T (by FFN.net standards, though it may fall under M or even MA here)
It's been
years since I've read it, and I don't recall the story clearly. So, the bumped ratings are just in case.
EDIT: After rereading the story for the better part of last night and early this morning, I'm going to go ahead and confirm that the story should be
rated: MA here... due to the graphic nature of some descriptions as well as some of the language used. So, it's off limits for YIMs/minors.