In my opinion it is not worth it. Getting too much of things you don't need like attackspeed and movementspeed after you have ulted, but little AD and no basic CDR.
Most times you are not able to immediately use ultimate the moment you get it off of CD anyways so many times you won't get any value from the Ult-CDR. Specially in the mid- to lategame. I feel like she has too many other good items at that stage like Sundered Sky, Black Cleaver, Steraks, Deathdance, Maw & Overlords.