Honestly I'm just a self-taught and a novice, so I do not have much experience. I do not knew the word おばさん, but I knew the word おかあさん and this has confused me. It seemed appropriate to make this observation to pure ignorant that I am. XD
Changed the definition as 小母さん is the regular lady you'd meet in the streets, not a member of your family. Usually written hiragana anyways.
Your aunt would be 叔母さんor 伯母さん but there is already a separate entry for that.