Sachi may suck as a VRMMO player, but she’s not stupid. It may seem degrading at first, but when one’s life is on the line, sucking up to more powerful people is a valid survival strategy. And she’s apparently quite good at sucking.
Similarly, eventually ditching her old guild for a more powerful player is also a rational move.
Read an erotic tale of one opportunistic player as she uses all her skills and attributes to survive the harsh reality of the SAO death game.