Welcome Delilah!
Other than Blandford's biography there is very little published information on Polly's personal life as it regards her music. The only thing I can think of is trying to dig up magazine interviews from the past 20 years of her career. I don't know of any central repository of these unfortunately. The old room509 site had a very good list of them (including their text), but that site is only available as an archive now:
http://web.archive.org/web/200805301602 ... frame.html(click the 'articles' link on the lower right hand side of the frame).
There is a very academic treatment of Polly's album Is This Desire which was published in 2002 as a couple of chapters in the book "Disruptive divas: feminism, identity & popular music" By Lori Burns, Mélisse Lafrance. You may be able to find the book used. I actually bought it and have considered scanning the relevent chapters. Google books will let you see some pages from it. It's really just the 2 author's philosophical and musical analysis of the album. There's no attempt at connecting the song's meaning to any events in Polly's personal life.
Another music professor published an article about 10 years ago on Polly also:
http://works.bepress.com/mark_mazullo/3/I've never seen the full text of this article, but I gather it discusses Polly's earlier albums.
The wikipedia article on Polly has a fair number of links to original articles:
http://en.wikipedia.org/wiki/PJ_HarveyMaybe some of the folks here can dig up their articles and post them. I will say she hasn't been at all helpful in the past at explaining her song's meanings and her personal life is off limits in all but the earliest interviews.