Can you still sickle cell if you're >3/4 white?

Yes: While sickle cell disease is most common in those of african, or african-american descent, one can still acquire the disease genetically based on their heredity.

Sickle cell: Possible, need lab workup to confirm or rule our.

Yes: If you have true SS disease you inherit a defective sickle cell gene from both parents. That means they both carried one defective gene ( in a pair tasked with making proper hemoglobin). It doesn't matter how far back in their family tree it started, or that it ever showed up before.