@Conjunx oh this is a cosplay and not art.
you can probably get away with cheaper materials since honestly Terezi made that outfit herself vs Redglare who probably got some real nice fabrics for her dope uniform. it also depends on how closely you wanna stick to the 'canon' design, Terezi's take on it is p. simple compared to Redglare.
i'm not fabric a expert but something simple to work with for the red portions with a cheap nylon bodysuit underneath (wear something above your underwear tho to avoid any accidental reveals since nylon can be thin).
doing her in a seer of mind outfit would also be fun.
@Conjunx i think paradox space has eridan in his flarp outfit; the one with the critical whale in it.
idk if terezi got confused for redglare when she's dressed up like redglare i'd think she'd consider it an honor. Just think of yourself as cosplaying a cosplayer.