What exposure is the kitchen window, Cheryl? I assume you open those blinds for an extended time?
I would expect the plant to really be root-bound. Being so, water just runs through quickly. There may be NO potting soil left. Talk about the potting soil being "well-draining"!
If you are going to continue to grow it "Bonsai" style, that will certainly retard its growth. If you repot it, say into a 6" pot, though you are not adding all that much potting soil and growing space, it will grow much faster. I guess it all depends on how you want to grow it, Cheryl.