Board Thread:General Discussion/@comment-98.218.70.24-20150317164438/@comment-3257939-20151022134121

There's also the fact that Yang herself didn't realize until she saw that picture. If it wasn't for that picture which was probably the same one we saw in the Opening then she wouldn't have realized that Summer is not her mother. After all, a picture of a person next to your mother, who looks more like you than your mother herself, is a pretty good hint.