Hmmmm... excuse me for saying this, but I wonder if you are jumping into buying your 2nd bike too soon. I know Grom is your first bike and have ridden it for 2000 miles, but once you get even more experience you won't care so much about being able to flatfoot. By the way, when you say flat foot, are you saying both feet or just 1 foot? I know girls who are shorter than you that rides R6's in its stock form.
If you were my friend, I would advise against getting a new bike just yet, and would recommend getting more experience under your belt. Being able to flatfoot only matters when stopped and going extremely slow. And it's during these times, where people most often drop their bikes.
Additionally, as time goes by you way want to explore other riding experiences. I know just riding around town on the Grom is hella fun, but it may get boring after time, and you may want to hit up the twisties. If so, messing up the geometry of the bike can have a negative impact on handling.
If you really want to lower it, shave the seat!!
Just my 2 cents from my personal experience.
EDIT: As an example, look at Dani Pedrosa.. he's only 5' 2" and he's a Motogp star... Marc Marquez is only an inch taller than you and he's a MotoGP champ. I know these are extreme examples, but experience goes a long way!