@gryffinnightwind You say she's in the YA stage, but is she close to aging up to adult? If so, she may be blocked from becoming pregnant until after her birthday. And of course if you already have eight sims in the active household, you won't be able to get anyone pregnant (at least not without mods).
Although I've never seen it happen, I suppose it's also possible that she has some cc clothing that's blocking her from getting pregnant. This is a common cause of sims not being able to age up, and the solution is to reassign the outfit or hairstyle and try the age transition again. You could reassign this sim base game clothing and see whether it helps.
If these issues aren't relevant, you might try an experiment. Save the household to the bin, quit to desktop, clear your caches, and start a new save. Place this household and see whether the sim can now get pregnant. If not, she may be corrupt in some way. You've already pretty much covered all the ways to reset a sim without mods, so I'm not sure there's another way to fix the issue.
By the way, an easier test to see whether a sim is pregnant is to tell her to "go here" on a random patch of floor or ground. Normally, sims child aged and older get a rectangle in their action queue with choices for walking or running as well as "automatic," as long as they're already standing on solid ground (i.e. not in a pool or something). But a pregnant sim will get a square instead, with no dropdown menu, just like a toddler would.
