A beautiful Australian thriller/drama
The Well

(1998)

Short Version:
 Katherine (Miranda Otto) did indeed have the money on her and she deserts Hester.

Long Version:
Conservative Hester takes in wild child Katherine as a helper for her ailing elderly father and grows extremely attached to Katherine to the point she gets jealous of Katherine's friends and buys her lavish gifts. Hester's father dies and she sells the family farm for money and moves into a small cottage with Katherine, stashing the farm money in the cottage.

One night when Katherine is driving she hits a young man. In panic, she and Hester dump his corpse down the old well. Hester realises all her money has been taken. A neighbour tells Hester he got burgled by a young man (the one they hit). Hester tells Katherine to go down the well and get the money off the corpse.

Katherine becomes mentally unstable at the thought of searching a soaking corpse, and believes the man is alive and loves her, then that he will kill her. She also produces a $100 note which fuels the distrust between the women.

Hester gets the well opening properly sealed shut by workmen. This is the final straw for Katherine, who deserts Hester despite the latter's protests. Katherine is shown to have Hester's money in her suitcase and hitchikes away, while Hester, madly trying to chase her down on foot with an injury, has to be taken home by the woman who bought her farm.

Thanks Meng!