Difficult to determine from the poor quality photo but looks to be a ZZ plat, Zamioculcas zamiifolia. A very popular houseplant, it appreciates bright but indirect light.......insufficient light can result in the leaves yellowing.

Also, if your sister has had it for several years, it very likely needs to be repotted and requires regular fertilization. As with ALL houseplants, it should never be watered on any kind of schedule but as the plant needs it. Water thoroughly when you do but then allow the soil to dry before waterig again.