She is the first person you see though. I've always thought they were referring to her.
Who else would they refer to? Yoda confirms it a movie later by saying: There is another Skywalker and Luke is telling the Force is strong in his family, my Father, me, my sister.
There is no way 'the other' Yoda speaks off is anyone other than Leia.
That's the obvious way to interpret that dialogue, yes.