I'm sure Mike C may have had his reasons for stating in his FAQ that "Jr." may be used by either males or females -- and perhaps times have changed to the extent where crossing such boundaries hardly matter any more.
But in proper etiquette circles, the suffix "Jr." is always considered masculine and is never used for a female person.
I quote the long-recognized (yet now deceased) maven of etiquette, Amy Vanderbilt:
"You hear it and you see it in print, but a girl should never be referred to as 'Greta McCarthy, Junior' even if her mother is a very well-known 'Greta McCarthy' whose name frequently figures in the social, business, or theatrical news and who, for professional reasons, may also be known as 'Miss.' It's too bad the parents didn't think to give the poor girl her own identifying name at birth to avert such confusion, but, as it is, the daughter may have her cards read 'Miss Greta McCarthy, second' or, if she prefers, 'younger' but she can't use the masculine 'junior.'"