Can you explain to me Angelique's progression through time in this non-linear fashion? 'Cos I've tried, and am again finding the head hurting.
This isn't too tricky if you have the diagrams to refer to.
Angelique from the parallel timeline (points B-H) is strangled by Barnabas; her spirit follows Vicki from point H to point A. As we saw, she managed to possess Roger Collins, who disappeared for a few days. During this time, she must have had him perform a spell that would restore her to physical life, much in the same way as David and Hallie brought Daphne back to life in 1970. Afterwards she caused Roger and Professor Stokes to believe she was "Cassandra Blair," an undergrad student at his college.
After Nicholas turned her into a vampire, she visited Diabolos in Hades and tattled on Nick. Her "reward" was having the vampire curse lifted from her; her punishment was being sent back to 1796. Still physically alive, she is sent back to point J, the second parallel timeline. We know this to be the case because Barnabas finds her there alive and well, with full memory of her experiences in 1968. He again kills her by having Ben set fire to her at point K.
In 1897 Quentin and Evan conjure Angelique back to life; this is the same Angelique who was torched at point K. We know this to be the case because when she meets Julia in 1897 she knows her from 1968. (The Angelique from the original timeline or the initial parallel timeline, points B-H, would not.)
Since Angelique is not destroyed (for a change) in 1897, we can presume she lives on up until the year 1970 when we find her married to Skyler Rumson. However, this implies an interesting paradox; some time during 1968 there would have been two Angeliques - Mrs. Rumson and an earlier version of Angelique who pretends to be Cassandra Blair. For all intents and purposes, Angelique this time avoids contact with the Collins family, knowing full well what's going on there. Renouncing her powers may also have been a tactical move in order to avoid alerting Nicholas to the fact that she exists in two places at the same time.
When Julia travels back to 1840 we find Angelique alive and well and making an annual pilgrimage to the mausoleum. This is the
original Angelique from the original timeline (points B-E) not the parallel timeline Angelique we've been following thus far. We know this because she has no knowledge of the future or who Julia is. It is also interesting to note this would indicate that Barnabas did not kill Angelique in the original timeline as he did in the parallel timeline (and in fact Barnabas never made any mention of such a thing). Perhaps in the original timeline, after Barnabas "died" Angelique accepted the money Joshua offered her and left town rather than trying to stake Barnabas.
She, the original Angelique, is killed by Trask in 1840. What is not explored, however, is the fact that upon returning to 1971 Barnabas and Julia would find the parallel time Angelique (Mrs. Rumson) alive and well.
This could also explain how Barnabas could fall in love with Angelique in 1840. She is not the parallel time Angelique who did all those terrible things we witnessed. It's possible that in the original timeline Angelique was not responsible for Sarah's death or even Josette's, considering Barnabas makes no mention of her involvement in either case in present day.