They control most of the wealth according to that non-academic report (the report is an advertisement for wealth management services), and I couldn't find an academic study that came up with a similar number. I should also note that the report doesn't say US women possess 51% of the wealth, they just "control" it, whatever that means.

Women do not accumulate wealth at an equal rate to men, one reason is that their salary is much lower (wage gap). A second reason is that most single parents are women and that pushes the wealth distribution for women further down.

In terms of ownership it's closer to 36%.

http://gender.stanford.edu/news/2011/shortchanged-women-and-...

It's especially bad for unmarried women who have about half the wealth of unmarried men. When you take race/ethnicity into account the gap is even wider.

http://globalpolicysolutions.org/wp-content/uploads/2014/10/...