I found this happened from time to time the entire 18 months we bf'd, my dd would prefer one side and feed longer than the other. I never pumped so I would start her on the low side (for as long as she would tolerate it), then put her on the fuller side, then again on the low side (she'd nurse longer then, once fuller from the fuller side). I found this would increase my supply and "balance" me out. Pumping is a good solution, and possibly easier than struggling to get lo to feed on the low side twice, as I did. Depending on age and size of baby and how long one plans on bfing for I would hesitate to go to one-sided permanent feeds. Once lo is bigger but not on solids yet they need more and it's nice to have the option of both sided availability.
Is your Ped concerned about her weight gain? If he/she is not, try not to fret about it. I know it's hard not to, my dd was on the 10% (or less) up until she hit 18 months.