@Tamerlane No, I think she stopped aging. Rob even mentions how she looks exactly the same.
If Alice was 6 when Sharon was 25 she had her at 19. Pretty young but not weird. More weird is the lack of mention of a father. I've always kinda suspected something going on about Alice's dad. Hopefully not Duke's grandpa cuz that'd get a little weird quick. But illegitimacy seems likely.
@DeusVult I didn't neglect the fact that she's stopped aging during that time, she was just gone for a decade. (Important phrasing, I know, but she's technically 35 that appears 25)
I don't have a precise age range for Alice and Sharon, which is variable on many factors, including if this takes place in the Victorian period or not. Hopefully she's around 16, because if she's 17+, things will get...weird.