this is in line with her positions and also the MA-tag. She's not a card carrying DSA member (only Tlaib is), was not endorsed by DSA and has campaigned for Warren in
prev elections. She's moved left since she got into politics but she's still more to the middle than the three (Tlaib being the closest to a socialist). Omar is also more traditional progressive liberal but her endorsement of Sanders is due to the centrality of foreign policy in her politics.
This is not a surprise nor is a wedge between her and the other three. The BDS vote was more of a wedge than this.
AOC got into politics because of Sanders, Pressley got into politics because of Joe Kennedy. That history sums up both current endorsements.