With the seat down as far as it will go, (I'm 5'2) the tips of my shoes barely touch the ground, but 5'4 might be okay. Also! my feet are 3-4, so maybe if she has large feet, this will make a difference too. I'm not confident enough a rider to not have major contact, I'd feel too wobbly. I'd recommend trying it out, if possible.
With the seat down as far as it will go, (I'm 5'2) the tips of my shoes barely touch the ground, but 5'4 might be okay. Also! my feet are 3-4, so maybe if she has large feet, this will make a difference too. I'm not confident enough a rider to not have major contact, I'd feel too wobbly. I'd recommend trying it out, if possible.