Hi, Donald. At that degree of relationship there's very little possibility of a confusion in ranges of shared DNA. The more distant the relationship is at each step, the more overlap and uncertainty we can see in amounts of shared autosomal DNA.
But if your mother's sister is a full sibling to her, you should share somewhere around 1700cM with her, approximately the same amount you'd share with a grandparent or a half-sibling of yours.
The next "level" down would be 1st cousin and would be half that amount, or around 850cM. This would also be the same amount you would share with a half-aunt, if your mother's sister was a half-sibling to her, for instance, the same mother but a different father.
One level farther and we're at around 425cM: a 1st cousin 1x removed; the same as a sibling of a great-grandparent. A 1st cousin will almost never share as little as 425cM with you, and a 2nd cousin would share around 212cM.
So the demarcations are pretty wide between full-sibling to aunt/uncle to 1st cousin or half-aunt/uncle. That's what I mean by little possibility of confusion between those ranges.
The different testing services report using different calculations for centiMorgans, but if your aunt is shown as sharing, say, somewhere in the range of 1500cM to 1900cM with you, she's your full aunt. But if in the range of around 600cM to 1100cM, there's a good possibility that she's your half-aunt.
