I think it’s very simple. At the end of the day both movements have the same common objective, which is equality. Weather we are talking about equality strictly between humans or between animals/humans, we all fight for the same thing.
The Ecofeminist movement sees a connection between the exploitation and degradation of the natural world and the subordination and oppression of women and other minorities groups. The way I see it, women (and other minorities groups) and animals are part of the same systems of inequalities.
The naturalization of women as inferior to men does not differ from the naturalization of animals as inferior to humans. Like for example, when we take into account the farming industry. Most farmed animals are female. They are tied to racks against their will and artificially inseminated by farmers. They are forced to give birth so that farmers can take their babies for food. They endure the pain of forced separation and search for their missing babies. They are used for their ovaries, for their bodies and when their sexual organs tire out, they are sent to slaughter while they are still children themselves.
Feminism is stronger when it supports the rights of all females, not just human ones. To restrict the feminist movement to only regard the rights of human females is not fighting for equality at all. So I firmly believe that veganism and feminism will thrive as a joined force.