Basically, it's down to, 'did she fall or was she pushed' off the cliff. Only the sharks know, really. And only if they were looking up instead of down. There is no doubt in my mind that Melissa made some first class -high octane -force 10 enemies, out of ordinary people who were betrayed and robbed with malicious intent, no other way of putting it.. It was malicious , Melissa's way of doing 'business'. Awful things happen to people who are treated like this, and it is on the record that quite a few of them knew they had been dudded, over many years , by Melissa. So motive is not hard to find, really. Motivation is another thing, opportunity a whole other thing, and method, yet another factor.
Lots of similar criminals strut round Sydney, free as birds , owing multiple millions to poor pensioners and widows, with nary a frown on their botoxed foreheads, very few take the off the cliff option. Rene Rivkin comes to mind, among the very very few who did. Although, he did it in the comfort of his mother's Milson's Point apartment. ...Not hurling from a height into unknown cold waters, hoping to miss the rocks, and other things underwater..
So it does happen, and maybe Melissa did have a Damascus Road experience that morning. To paraphrase Colonel Nichols in closing moment of the film, The Bridge on the River Kwai... ' what have I done? '...... Perhaps. Improbable, but not impossible.