I noticed that there was some discussion about the title.
マ男ニ染マル純白ノ彼女
マ男 refers to man other than her husband with which she has a carnal relation
染マル means getting dyed
純 means pure, naive, chaste, etc. while 白 means white
彼女 means girlfriend or just girl
So at this point we can get a rough translation of "The pure white girl/girlfriend gets dyed by men other than her husband with which she has a carnal relation". Sadly, this masterpiece of a title is not destined to see the light of day.
Now the title "She's a pure white girl" is coincise, which is good, but it fails to convey that her purity is going to get corrupted and clearly it has some bad connotations in the english language, even if they are unintended.
If we want to get the most with as little change as possible, we could change the title to "She was a pure white girl". The "was" alone implies that something has happened/is about to happen to her whiteness.
Since "pure white" doesn't convey enough the meaning we are going for and at the same time it has too much meaning we were not going for, it's time for a change. For example "She was immaculate". Simple and elegant.
If you want to to be more poetic, you could go for: "Like a lily blooming in the mud" with the lily being a classic symbol of purity
If you'd like to have a more joking tone, you could have "She was pure, they were not" (read by that guy from honest trailers).
I wrote this post because I wanted to point out how interesting can be the process of translating a title.
Now go change the title to one of these options or make an even better one yourselves! ( •̀ ω •́ )✧