some plank plowed into the back of us when i was a kid-gave my mum whiplash and brought on arthritis in her neck something like 15 years before it should have appeared
it may be a little niggle now but get it fully checked out as it could really bother you in later life
as for claiming, up to you really-but
imo sun or not she should have had control of her car which includes being able to see at all times