April is a key figure.

Her mother's motives and ambitions all include her daughter, as she has starred April in all her films. She may be the one person her mother would trust to hear difficult truths from.

I don't recall any mention of April seeming oblivious to the fact that things may not be going well, that her mother may be being taken advantage of, or in danger of being taken advantage. Or that her relationship with her mom isn't close...

It's not clear though if you have worked with her personally if you are doing post production, or how well she may or may not know you. It would be to your credit to approach April and layout the problems, and given the fact that you actually would (in the short term) personally gain from her mother's mistakes, that an effort to try and enlist her help to prevent her mother from making the mistakes which you would financially gain from, could gain some trust.

A plus would be if you don't also hit on her. :)

Once the problems or current obstacles are laid out (you may have needed to leave out some of the prior detail that may put her mother in too terrible light and make her feel defensive for her mother) you then discuss possible solutions.

Together you come up with (even if you lead her, she'll need buy in and ownership in the choices) at least two reasonable options to present to her mom. This she will talk to her mom alone, but bring you in to help when her mom is ready to hear more details about what she can do to begin to stop the train wreck.

The mother is able to listen to her daughter, and you, and possibly put aside the rush job, concentrate on getting an appropriately edited version (so you ultimately forgo your short term gain in favor of the groups's needs).

The internist producer gets a more sober and realistic view of the present circumstance that can only help the outcome now and in the future. Trust is strengthened rather than further strained. You don't always have to let people go over the brink for them to learn. Sometimes you just have to point out to them, that they really are on the very edge, and hope to god they listen.

Am I close?