Or some other girlfriend of Mick Jagger?
My understanding is that it wasn’t written by her, she was simply chosen to sing it (It was written by Jagger and Richards). So no, it’s not about one of her miscarriages. In fact, reading the lyrics, it doesn’t suggest miscarriage to me at all.
Me neither, where did that idea come from? She was a druggie and party girl, I don’t think she would even have noticed a miscarriage. at least an early one.
The Jagger song that famously references Marianne Faithful’s miscarriage is “Memo From Turner,” which includes the lines:
The baby’s dead,
My lady said.
According to Wikipedia, “As Tears Go By” was one of the first Jagger/Richard compositions, and allegedly written because their manager kept insisting they write songs…and asked for something “enclosed by walls.” Supposedly manager Oldham also changed the lyrics from “as time goes by” to “as tears go by.”