(there's mention of rAma's sister in this kriti - pardon my ignorance, who is she?)
vishNu s(ah)OdarI - vishNU's sister - pArvatI/yOgamAyA
And that is why, in mInAkSi tirukalyANam, since her father (maladhwaja pANDiyan) was no more, her brother, vishNu gives her away.
The motif occurs in several compositions - starting with ANDAL's dream about her wedding where she says 'maNamAlai andari
SUTTa kanA kaNDEn tOzhi nAn' - traditionally, the to-be sister-in-law performs this.
pArvatI is referred to as rAma sahOdari/krishNa sahOdari as they are but different forms of vishNu. SyAmA SAstri uses it cleverly with his mudra in many compositions - SyAma krishNa s(ah)Odari to refer to pArvatI.