An Author without an Affiliation We are preparing a manuscript to be submitted to a peer-reviewed international journal. We have an author that contributed significantly to our research work in which we would like to include her as a first author of our manuscript. The main problem is that she doesn't have an affiliation. 


Our question is to advise us please under what institution should she be affiliated? 
Can we list her as a first author without an affiliation? 
What type of institutions other than research centers and universities could  generally be listed as an affiliation on a research paper?


Thanks a lot!
You don't need an affiliation to publish. Independent Researcher or the equivalent is enough. You probably need an email address, but likely a professional one, separate from one used for personal things. That isn't really essential, but might be helpful.