With that schedule - it is possible. She may enter both, max out in the steeple and then decide on whether to scratch from the 1500 heat at the last minute based on how she feels after the steeple final.
15/08 10:50 W 3000 Metres Steeplechase Heats
17/08 20:30 W 3000 Metres Steeplechase Final
18/08 12:05 W 1500 Metres Heats
21/08 20:00 W 1500 Metres Semi-Final
23/08 17:00 W 1500 Metres Final
According to http://www.iaaf.org/wch09/results/eventcode=3658/
15/08 10:50 W 3000 Metres Steeplechase Heats
17/08 20:30 W 3000 Metres Steeplechase Final
18/08 12:05 W 1500 Metres Heats
21/08 20:00 W 1500 Metres Semi-Final
23/08 17:00 W 1500 Metres Final