I've often wondered why you don't see Lidl sucking up to Amelia. I would guess it's because she knows she can't be the 'top dog' in terms of class and wealth. Amelia (I know she can be annoying) has a natural grace about her and because she was born into wealth, she doesn't brag or try and out-do anyone. Lydia would know this and I'd imagine, make her feel rather insecure. Lydia likes to dominate in her relationship and friendships - you can tell by the way she belittles people calling it banter, pokes fun at Carrie and Cal's cars so she feels more superior, calls Ali 'good boy' in a patronising way and highlights any mistake he's made or difference of opinion (the paint on the drive and when he called the spare room paint 'magnolia'). She would hate the fact Amelia doesn't have to rely on sponsorships to furnish her house or a brand trip to fly first class and couldn't pull off the Lady of the Manor routine with her.
I think the same goes with Sophie Shohet; I could never see them being friends as Sophie would see straight through Lydia in a flash, Sophie can buy her supercars outright with cash, has her own successful business, rarely does anything sponsored and if it is, she's beyond clear about it (and has made it clear she has no time for influencers who try and give the impression they're rich and buying all these designer goods with their own cash, when it's all bought with vouchers and sponsorships) - she's everything Lidl wishes she was.
So she sticks with Carrie, because she's her boss and strategically forges friendships with peers she thinks she can benefit from in some way - i.e Vic and Leonie - probably for their Dior sponsorships!!
) 
