No. An Aunt is too close – she shares a lot of DNA with your mother’s mother which came from their parents. Since they are so close, and have long stretches of identical DNA, it’s possible to get 150cM that is split between the parents of your mother’s mother and your mother’s aunt. In many respects we need to treat an aunt or uncle just as we would a parent. Perhaps think of parents with two children (you mother’s mother and her aunt) – they each get big blocks of DNA from their parents – some overlaps, some does not – but the part that overlaps, could be part from one parent and part from the other. Use triangulated groups to sort out the 150cM stretch of DNA.