Been there, done that, bought the ill-fitting T-shirt which looked better on my sister.
I'm one of six girls, and we're of varying levels of attractiveness... but my oldest sister was and is gorgeous. People commented All. The. Time. At Uni, where I ended up doing almost the same degree she'd done two years previously, lecturers would say "Oh, you're ---'s sister? I had no idea! You don't look anything alike! She's so pretty!" Uh, thanks.
I think I was hyper-aware of any favouritism my parents showed because of the comments of strangers. They probably didn't say much about it, but I felt like they did, you know? I also had issues with my next oldest sister, who was very skinny. Looking back she was scarily, skeletally skinny and my parents were always worried about her and trying to fatten her up. But at the time I was ashamed whenever people would comment on her weight, because I felt it was a reflection on mine. I tried to eat less so I'd be as skinny as her, and I hated having underwear in a bigger size than hers (of all the things to obsess over!). The funny thing was, I was NOT a chubby kid. I just had this idea in my head that being "fatter" than your older
sister was the worst thing that could possibly happen.
To be honest, I'm not sure how they could have handled it differently. It wasn't their fault my sister was prettier than me; it wasn't their fault strangers commented; it wasn't really their fault that if I overheard them saying "--- is so pretty" I took it like a knife to the heart, because that wasn't a particularly rational response of mine and who'd have predicted it? So sadly, I don't have any solution to your worries. Life isn't fair. If your daughter does turn out homely people will
notice, and they will
make stupid or hurtful comments. And whether or not she's affected by it will be largely outside your control, because it depends on her personality as much as anything. It sucks, but that's the way life is. (And to further be a downer, she may not end up gorgeous after the "awkward phase" either. Not everyone does. I look better at 23 than 13 because I'm somewhat cluier about hair and clothes, but no quantity of cheekbones I might magically acquire in my 30s will turn me into model material. I'd need some radical facial restructuring that age doesn't tend to impart! I think the whole "If you're ugly as a child you'll be a pretty adult thing" can be really heartbreaking for those who stay plain.)