So, i want to get my little sister a road bike for christmas, but she is vertically challenged... only 5' tall. And i am not sure about frame size... is a 48 cm frame small enough? I know all frames are different and whatnot... but would this be an average good size? whatever i get, it will most likely be a CL / Ebay purchase so i would be buying sight unseen. can anyone lend any info on this subject?