actually in Sino-Tibetan languages, "Mu" is widely used as female. For example, in Tibetan language, 拉姆, which is pronounced as "La Mu", means fairy, 觉姆, pronounced as "Jue Mu", means female monk. Also in traditional Chinese, 姆 refers to female.
I think when it is used in foreign names, it actually has only pronounciation similarity, and has no relationship with its traditional female meaning. Actually this is fairly common, for example, "humor" which is translated as "幽默", but 默 in traditional Chinese means silence.