Last year, the owner of the club in my hometown (Real Salt Lake) brought in an NWSL expansion team (the Utah Royals). From the start, he made it clear that the new women's team would play all its games in the main stadium. He's spent a fair amount of money on advertising, facilities (dedicated women's locker rooms and housing, for instance), and youth development for local girls. In the context of women's professional football and its obvious ceiling, his strategy seems to be working. This season, the Royals have averaged 11,525 attendees per game. One match attracted more than 17,000 people. Not a sellout (the stadium holds a little more than 20,000) but enough to keep some semblance of a real atmosphere in a larger venue. Because the players earn such low wages, and because the club has attracted a number of (probably modest) sponsorships, some in the local media have speculated that the club is coming to close to breaking even in terms of spending/revenue. I don't know about that, but this wouldn't even be a conversation if the club played at the development team's venue, which only seats about 4,000.
Now, England is not the USA, and Goodison is a lot bigger than RSL's stadium. It costs a lot of money just to operate a 40,000 seat stadium. But I really think that if Everton are serious about nurturing their women's team long-term, they should play some games at the larger venue with an eye to eventually making a permanent switch. As the above poster suggests, this should be seen as a marketing strategy at first. Free or very, very inexpensive tickets at the Goodison games, with lots of advertising. Increase awareness, etc.