Did she ask for your help? It was too long for me to read. And too short to explain the range of issues you raise.
But helping someone buy 'the right bike' is a commendable effort.
Good luck and happy miles to sister.
re-read edit: fat 650b tires at lower pressure are not as fast as 700c at higher pressure, given equal engine output.. Not that it matters to Sis.
__________________
Vintage, modern, e-road. It is a big cycling universe.
Last edited by Wildwood; 11-16-20 at 09:44 AM.