According to her parliamentary profile she lost her position as critic for post-secondary education in 2012, after less than a year in the position, and didn't have any shadow cabinet position at all until she was given two associate critic positions in early 2015, a few months before the election so regardless of the "rising star" spin in the media it doesn't look like she was thought highly of within caucus (or at least by the leadership).
She was appointed to that critic position by Layton before he passed on. When Mulcair was elected leader, he shuffled some of the critic appointments. When the shuffle was complete, I guess she found herself with no critic role.
Rathika endorsed Peggy Nash for the leadership only after Peter Julian said he wouldn't run (she was an early backer of Julian for leader when Jack died.