Well, either God knows the ultimate end of a human and her soul He has not yet created, or He doesn’t
You may note that I didn’t say yes or no in reference to the original question, but specifically to your quote here:
And yet He still creates this person
In summary though, I do acknowledge that God does know the ultimate end of a human and his/her soul. I omit the last part you included though, as I already illustrated that there isn’t necessarily a soul that hasn’t been created yet.
My point in the response to the second quote was that the conception of human beings is more or less on the shoulders of humanity, aside from however God started the first of us. It is through human bodies that we mate and conceive, and God simply obliges the fact that we conceive by creating a soul for the person being conceived.
If as is being claimed here He does, then I have to ask why create a creature He knows is going to end up in Hell
If you bear a child and you know he/she will grow up and never meet you, or possibly hate you because of a misunderstanding, it isn’t a reason to prevent him/her from living and experiencing life. That is basically exactly what it is with God, at least as far as I am aware. God doesn’t send people to hell so much as people send themselves away from Him. Damnation isn’t so much an example of becoming evil as it is an example of depriving one’s self of good. An absence of good is basically all evil is - the difference isn’t of two separate entities so much as the difference between existence and absence. That being illustrated, even though God knows someone will go to hell (knows a child of His will hate Him and move away from Him) He still respects the fact that that’s his/her decision. Hell/damnation is just more or less a result of the fact that souls deprive themselves of God, who is the source of both life and love in a place that is apparently absent of it.
I understand the free will argument and the stuff around predestination, so I’m not saying God predestined her to go to Hell - the point is, and the claim is, before she existed, before He created her soul, He already knew she would, for whatever reason, end up in Hell.
I think any response to this would tie in with my response above.
As an example, if I have a child and he leaves me forever before he can support himself - then okay, fine, he can have his way.

Of course I don’t want him to - I would probably be devastated. I would force him to come back under my roof where I have every necessity for him to grow into a well-nourished individual;
but I brought him into the world and he had the freedom to choose his destination. He wanted out so he got out. Same concept, basically.
So I have to ask, what was the point, since the creation of this particular girl’s soul will result in another soul languishing in the horrors of Hell for all eternity
The point is that it was that person’s choice, not God’s. For all future reference, there isn’t a soul in hell that hasn’t paved the way. We believe the way a soul does that paving is through mortal sin, but the circumstances for that are different with every individual on earth.
Unless of course, God didn’t know, and couldn’t know, because of our free will, but that would mean God isn’t all knowing
The fact that God knew something bad would happen to one of His creation (due to it’s own decisions) doesn’t mean anything insofar as His fidelity to His own goodness or His overlook of time. The only way God could keep any souls from going to hell would be to 1) inhibit man’s free will, or 2) not make any souls in the first place, thus also keeping all souls from getting to heaven.
Assuming either of those happened though, there wouldn’t be much point to being an infinitely intelligent, powerful, morally sound, expanding, progressing source of contingency.