I'm going to start with basics...
Rather than "What needs to happen here?" let's try "What is
According to EL314, the majority of women on dating sites are looking to marry, with or without children from a prior relationship. Idealist suggests that cultural images of marriage and relationships push women to seek marriage.
As someone about to get married, I'll throw in that there's over a thousand legal benefits to being in that state in the U.S. (no clue worldwide), nevermind the social ramifications. Though there's lots of history leading to women wanting a ring and a white dress, it's also the mainstream model for meeting one's goals. You get a ring, and you have someone to split the bills and the chores and bitch to about your day, with sex thrown in as an added bonus.
I guess it depends what kinds of difficulties she's having.
I mean, if you're having trouble meeting someone who has the same interests as you, same goals, sexual attraction, is responsible enough to be a good role model for your kids and a reliable parent, and that whole package, then it's going to be just as hard if you're poly.
Perhaps you were talking about the notion that by opening her options to the poly dating pool, she might be able to find more compatible mates? I guess that's possible, but the poly dating pool is so small, adding those potential partners is a bit of a water drop in the bucket.
Thing is, maybe relating in a poly way would free the everywoman from having to get all her needs met in one place. Even if she can only find one partner, and even if they call it monogamy, maybe she realizes that it's okay for the relationship to not be her One True Perfect Relationship, and that it doesn't need to meet all of her needs. That alone would be pretty awesome.
As for giving relationship advice... I'm openly poly, so I do my best to give healthy advice, and to keep in mind that my friends are asking ME for advice because they want MY advice, either as a semi-level-headed person or as a polyamorist, and respond accordingly. I do in fact proselytize about poly, but usually not in moments of advice-giving. I'd rather just live my life and have it be good, and have people see that as my testimony, not my words.
PS-- I totally want men in on this discussion. Maybe it's just me?