I agree with Celsa's assessment. (view spoiler)[I went back and re-read the end of the book trying to answer this question myself and the statement "Irene wasn't sorry" locked it down for me. If she hadn't given her a shove, this statement wouldn't make sense.
Also, her first instinct was to hide rather than rush down to check on Clare, and when she does finally go down she's thinking about what others will think, not worried about Clare. In fact, she has a panic when it occurs to her that Clare might have survived - indicating that she for sure wanted her dead (as a single lady Clare would have been a threat) and maybe even that if Clare were still alive she could tell everyone she'd been pushed! (hide spoiler)]
Also, her first instinct was to hide rather than rush down to check on Clare, and when she does finally go down she's thinking about what others will think, not worried about Clare. In fact, she has a panic when it occurs to her that Clare might have survived - indicating that she for sure wanted her dead (as a single lady Clare would have been a threat) and maybe even that if Clare were still alive she could tell everyone she'd been pushed! (hide spoiler)]