Re: size 2
In the US, clothing for women is sold in sizes. Size 2 is a VERY small size, although most of the main characters on tv shows are usually sizes 0, 2, or 4.
(When Dove ran an ad campaign with size 10 women, men said they didn't want to see "fat women" despite the fact that the average woman in the US is actually a 12 or 14. Yes, we're an overweight nation.)
A size 18, though, is really quite large.
This is not exact, but it's close enough for this.
Extra small: 0 or 2
Small: 4 or 6
Medium: 8 or 10
Large: 12
Extra large: 14/16
Extra, extra large: 18 and up.
She went from being very, very slim to very, very heavy.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.