Walter Payton used stronger together before Hillary.

CBS second episode of Super girl is titled "Stronger together" also, maybe she got it from the TV guide

http://variety.com/2015/tv/news/supergirl-episode-2-recap-1201632124/

http://lehmannstrobel.com/articles/title-and-trademark-clearance/
Posted from my iPhone/Mobile device
I am not sure how it works but...

http://cocatalog.loc.gov/cgi-bin/Pwebrecon.cgi?Search_Arg=stronger+together&Search_Code=TALL&PID=y5IrHkvQAA_G00pOc9RFd7Ou509&SEQ=20160726165330&CNT=25&HIST=1

Was this before or after her campaign manager resigned???

Either way it sounds like mimicking sound bytes from more trusted and influential people!