Rarity as a mother figure · 4:32pm Aug 14th, 2015
From what people have told me, there don't exist too many stories with Rarity being in the role of a mother figure. Well...putting it a better way, when it comes to adoption stories such as this one, more than likely, one of the main six is going to be used as the main mother figure for the foal introduced into the story. And from the looks of it, Rarity seems to be used the least for that role.
Why?
From what I've seen, the pony that seems to be used the most for stories like this is Fluttershy, which is understandable. Fluttershy is naturally kind and caring, as a mother in these fics should be. But when I took into consideration for planning From Savage to Civil, I figured "Yeah, Fluttershy would normally be a good pick for this type of thing, but it has been done SO MANY TIMES; I wanna do something different." So I looked at the rest of the Mane Six and found that Rarity had almost nothing in common with this feral colt I was making for this...
Considering that I love writing comedy brought on by contrasting personalities, I think I made the right decision. 
My point is, why is Rarity used so little for these types of stories? She's just as capable of taking care of a child as any of the other members of the Mane Six, so why is From Savage to Civil one of the very few fics where she's in this role?
I actually don't have an answer for this. This is an honest question.
Probably because she is seen as the prim and proper worldly mare who wouldn't make for the best mother. That one woman in the circle of friends who doesn't do the parenting thing like the rest of them do. And she and AJ are the two most obvious 'working mare's' in the mane6. Pinkie as well, but she goofs off so much it's more like she works part time.
Back to Rarity and Applejack, Rarity's 'family' episodes have been more her pushing aside family things to focus more on business type things, where as AJ has been shown to make business and family sides of the same die.
Fluttershy is the obvious motherly one. Applejack is the chore heavy but very caring mother. Rainbow is the awesome aunt, but has potential to got both caring or negligent, and is sorta of neutral over all. Twilight is the education scheduled mom. Pinkie is the fun mom. Rarity tends to be the business-centric mom.
Maybe because Rarity tends to "faint" too much. But you need to think that is not like it don't exist, some stories put Rarity more like a mother figure to Sweetie Bell because their parents are usually away.
I imagine Rarity as her elegant self much of the time, but at heart, she's a caring and thoughtful person that will show that whenever needed. Such as when dealing with Sweetie.