I always lived by the rule that there are "fixed points" (per Doctor Who!). Kagome will always on her 15th birthday fall into the past. She will have the Shikon ripped out of her. She will always break the jewel and find the shards.
So by this logic:
Kagome stays in the Sengoku period and dies. Years later she will be born with the Shikon because 50 years prior to her falling in the past Kikyo was burned with it. She will get pulled down the well, break the jewel, fight and kill Naraku, stay in the past and die. She will be reborn again in the future and continue to the loop. I see no reason for her to remember any of it - she didn't remember her life as Kikyo after all.
The only way this would change is IF she stopped the jewel from burning with Kikyo. If time travel
were real then it would always be a loop.
If I decided to pop back into 2010 and on the day I graduated, I would be getting ready in the morning, eating bfast with the family, etc. If I decided to pop back on the day again, the same thing would be happening, unless I jumped back further and told my younger self to drop out of school.
I don't see the timeline changing because the jewel will always burn with Kikyo.
Is Kagome her own ancestor? I don't think so because then she would have a very, very diluted demon blood in her unless it was completely bred out of the family. I like to think that one of the other shard hunters took the name Higurashi or maybe it's completely unrelated and her ancestor is wandering the past without her knowing him.
BAM. There is my addition~ >