How well do you know the girl's mother? If this girl's social awkwardness is indeed at least partly an autism spectrum thing, she could probably benefit from a social group and might even qualify for such services through the school district. So if you feel you know the girl's mom well enough, you could try mentioning that you've noticed that her daughter seems to be trying to exclude other kids or put them down, and you're worried that her behavior is alienating her from other kids. Or if you feel uncomfortable doing that (and it is an uncomfortable thing since parents can often be defensive about what they perceive as criticism of their child or parenting even if it's well intentioned) - since you mention you've observed this in the classroom, you could mention to the teacher that you're concerned about this girl's behavior - both because of how it's affecting other kids' feelings and how it's harming her by alienating her from other kids
good luck!
PS: Brenna has some great suggestions about helping your daughter evaluate this friendship. In addition, though, I'd compliment your daughter for trying to be friends with a difficult person. I wouldn't want your daughter to be a doormat to this other girl, and if things don't improve with this girl you definitely need to help your daughter make a healthy decision about setting boundaries with this girl, but as a mom to a girl on the autism spectrum I applaud anyone who can look past someone's social awkwardness and try to make friends with them instead of just dismissing them as "weird".