I've heard so much about marrying an RM, marrying a man who can take you to the Celestial Kingdom, etc. But what happens to girls who can't have children even if they are faithful LDS? Where do they fit in if at all?

They are just probably constantly reminded how they can give birth to a ton of spirit children in the celestial kingdom.

If they are authors who write favorable biographies of prophets, they give you callings in the upper-echelons of the church. ;)

The same thing that happens to every other person/group who doesn't fit the perfect LDS "mold" - they're marginalized or ignored. Sometimes systematically shunned.

They just really don't know what to do with those that don't fit "the plan" - gays, singles, infertile, etc.

I've known quite a few TBM families over the years where all of the children were adopted. One family in particular that was quite large was my Nazi-TBM Seminary teacher's family. I didn't really know any of his kids though because his older active kids didn't live in the same city, & his younger kids (still way older than me) were completely inactive. He & his long suffering wife were always working overtime to prove to people that they were just as good as anyone else even though their kids were all adopted.

Who had five or six little kids and she was always FRAZZLED.. I heard her say on more than one occasion while teaching RS lessons that the role of single or women without children was to help out those who had kids. Go over and watch somebody elses kids for an hour so a frazzled mom could get some sleep or have some time to herself.

The thing that got me the most was that this lady really was an extremely nice woman.. She truely didn't know what she was saying was offensive.

false pity. And when they can't stand that any more and think they're going to go insane, the bishop calls them to work in the Sunbeam class.

This post gave me an odd vision of the Celestial Kingdom.
So you can't have kids down here but you go to the CK and can have lots and lots of spirit offspring.
How in hell does this happen?
Do you have a cubicle where Peter Priesthood visits and gives you a deposit, adjusts his robe and goes about his business?
Does he wander from cubicle to cubicle looking for Mrs. Right for his seed?
Thinking of the Mormon concept of eternity gets more ridiculous every year.

The ward's brood mares who have piles of kids and live in poverty as a result will resent her and constantly remind her that their having kids outranks her having a career, even if she only works because she doesn't have kids, and not the opposite. The very definition of Hell is " an active LDS woman who has fertility problems".