The plot will allegedly see Janine walking out on her husband Michael Moon (Steve John Shepherd) and their child Scarlett, according to The Sun.
Charlie Brooks will be leaving the BBC One soap for six months later this year, fuelling rumours that she will take part in this year's Strictly Come Dancing.
Janine will reportedly be seen leaving London with a suitcase containing £450,000 in cash, after she decides to tests her husband's commitment to their relationship.
An insider said: "The storyline is action-packed. Janine and Michael have always had huge trust issues, and their wedding and the birth of their daughter last month has done nothing to change that.
"Things come to a head when she accuses him of seeing another woman, which he denies.
"She then demands to know why he forced her to rip up their pre-nuptial agreement before their wedding and then she gives him a big test.
"She tells him the case has £450,000 in it and says he has to choose between her and the money. She leaves the cash in the kitchen and says if it is still there in the morning she will know he loves her.
The source added: "He is seen clutching the money, leaving viewers guessing as to what he will do next.
"The next day the money is still there - but in a massive twist it is Janine who ends up deciding she can't stay because she feels she is not fit to be a wife or a mother.
"She decides to leave Albert Square and Michael - but the big question is whether she will take baby Scarlett with her."
Brooks is said to have filmed the scenes in question earlier this week. Her exit is due to air in September.
The actress said last month that she was "lucky" to be granted time off work from the soap.
Watch Janine's EastEnders character trail below: