Mistral has the slimmest barrel on the market. You are governed by the fact that they need a cartridge or converter so the section will have to accommadate that size.
Get the barrel nice and not fat and ugly and you'll end up with a slim pen.
Don't overthink that because its for a lady it needs to be smaller.
Kitless sections are a lot thicker than kits pens and the "Ladies" buy them