You'd have to lift some serious weights and regularly, and probably at medium reps, and eat **** loads and...BE A MAN to start adding thickness to your waist. Which again isn';t very much. You, a girl? not lifting very much? Would struggle to put on muscle if you tried your best anyway?
Seriously.
I'd do RDLs because they feel a lot better to me and hit the posterior chain more than the lower back imo, but either will do.