Should you ever use a nickname as your ancestor’s given name?

Purists would tell you that you should use whatever is on a birth certificate as an individuals “given name” in your genealogy database. Sometimes I think some discretion should be used. My great-grandmother’s birth certificate lists her as Francis Rampley. However, every document she signed from her marriage document through records settling her husband’s estate lists her as Fannie Neill (her married name). Her tombstone even has Fannie Neill listed. Consequently in my database her name is listed as Fannie as apparently that is what she wanted to be called. In my notes there is information about her birth certificate and the name it actually lists.