even if you hand express to get some of the pressure off that boob, iif you dont you could get mastitis so getting it soft and the milk flowing, hopefully into her :)
most babies do have a prefered side, as your milk has come in you need to massage it and express some milk so its not as full, I would keep offering her that side fist, express some milk so its not so full and so you have some on your nipple so she can taste it., just keep perservering with her so she gets used to that side :)