For video games terminology, what is the proper translation for "range"
In gaming field, (of) long range is commonly translated into 远程 or 远距离, and ranged attacked is 远程攻击. You can use 射程 when you want to express the notion of range.
By the way, 主力 is not the right word for strength. If you use 主力 here, it means primary (attack method). To say strength you may want to use 强项 or 优势.
So I would translate this way:

&quot;The great strength of Annie comes from the long range of her fire ball.&quot;
安妮最大的优势是她远距离的火球。