Okay, so I opened my apple and found sprouted seeds, so I planted them and now have seedlings. From what I can tell, the Pink Lady can be self fruitful. Does that mean the tree will produce true if I keep it away from other "parents"?
You are unlikely to get apples like Pink Lady from your seedling. Even if self pollinated the fruit won't be the same as the parent. But it would be interesting to see what kind of fruit you do get.
If you have the apple tree, just take a cutting in early spring.
That is before the buds open.
Seeds are produced via plant sex. The seeds from that apple certainly have Pink Lady for a mother, but some unknown variety for a father. Often times it is an inedible crab apple that does much of the pollination for the big orchards. So the resulting fruit will most likely be nothing like Pink Lady, just like a human child is different from its mother. There might be some vague similarities, but... probably very different.