Heres a thing I thought/theory . In the first white trailer for season one of RWBY think of what weiss was fighting, it look similir to what weiss and winter can summon, because it is. In the white trailer for season 5 (or volume) weiss is fighting some more, she does not have her scar (witch she gets in the season/volume 1 white trailer) and we can see when she has one she can’t fight she calls out Winters name and is disappers. We can think in both white trailers WInter was training her sister.