I think recent investigations say that we have combined two different women into one.
The parents/ancestry of Geva, the wife of Dirk van Holland, are Unknown See for instance Cawley's entry for her, but previously she had been thought to be the same as Gerberga the daughter of Meginhard (IV?) of Hamaland and that is still in some of the Wikipedia pages for Dirk I (see Netherlands and German versions).
Gerberga the daughter of Meginhard, is supposedly the mother by an unnamed husband, of Wichmann who inherited Hamaland from his grandfather - see Cawley, again, which is disputed by others, but there are definitely no primary sources at all that indicate that Wichmann is the son of Dirk of Holland. Given Dirk II of Holland, and Wichmann married half-sisters, than you would expect there would be some reference to them being brothers if that was the case.
I think we are never going to know for sure but I would turn the two profiles for Geva/Gerberga, into two different women. Geva the wife of Dirk of HOlland with unknown parents, and Gerberga as daughter of Meginhard, possibly the mother of Wichmann.
(There is no evidence for Geva's marriage to Gerulf, who is possibly Dirk's father, so I would definitely disconnect her from that marriage).
