Usually people who attempt suicide don't do it on impulse.
Normally, a suicide victim would engage in planning the act, most go to great research in order to follow through on the chosen act.
There can be weeks or months of preoccupied, morbid thoughts about suicide and although the planning and intent is usually a closely guarded secret, there are usually 'clues' picked up by loved ones who are close to the depressed individual. Especially if a close relationship is involved.
Libby had just gone back to Uni from home.
Her Mum said they were very close, and I'm sure her Mum would have picked up on any nuances in her mood, but said she was happy.
There was no evidence that Libby had researched suicide recently online or anywhere else.
I think it's the way the defense seized on the 'throwing myself in the river' that struck a cord.
This was obviously done on purpose to 'register' prominently in the Jury's minds as I'm sure in the past that Libby may have discussed other ways of suicide too. But the defence chose that one method.
I think it's highly unlikely that Libby put herself in the river.
This comes from my own experience in those matters, professionally and personally and having friends and family who have taken their own lives.
JMO