EXCLUSIVE: Maggie Fights With Meredith Over Her Dying Mother in Dramatic 'Grey's Anatomy' Sneak Peek

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Is Maggie about to lose her mom?

On Thursday’s episode of Grey’s Anatomy, titled “Be Still, My Soul,” the health of Maggie’s mom, Diane (LaTanya Richardson), continues to deteriorate -- and the trusted doctors at Grey-Sloan Memorial Hospital are at odds over what to do.

In ET’s exclusive sneak peek from the episode, which marks Ellen Pompeo's directorial debut, Meredith (Pompeo) and Maggie (Kelly McCreary) butt heads over how to proceed with Diane’s breast cancer treatments, which aren’t producing the results they were hoping for. So dire is Diane’s outlook that it’s starting to affect other parts of her body.

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“This protocol is making Diane so sick that her esophagus tore,” Meredith warns Maggie, who chided her half-sister for trying to change her mind about treatment options.

“That could just be from the cancer,” an anxious Maggie says, defending her decision for her mom go through an unproven new trial.

“You can’t wait to get her to her next infusion,” Meredith accuses, worry spreading across her face.

“Because my mom wants to live and this clinical trial could give that to her,” Maggie desperately responds. “She wanted to do it. She could have said no.”

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Meredith tries to explain that sometimes it’s better to let her mother make her own life decisions, without her hovering over her. Maggie, though, doesn’t see it that way.

“I just need to get her to the end of the treatment,” Maggie says, prompting Meredith to fire back with the harsh truth: Her mother is already dying and won’t make it to the end of the treatment. “She’s suffering because of it,” Meredith attempts to reason.

That’s when Maggie hits a nerve, striking Meredith where it hurts most and bringing up her late mother, Ellis Grey, who died in season three.

“At least I’m doing something, at least I’m not just giving up and saying no,” Maggie says angrily. “You don’t get it! You wouldn’t. Meredith, I love my mother enough not to say ‘Screw it!’ and throw her down a damn drain!” Watch the dramatic confrontation in the exclusive video above.

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ET was with Pompeo at PaleyFest earlier this month, where the 47-year-old actress spoke about going behind the camera for the very first time.

“It was a lot of work, which is why I always resisted in the past,” Pompeo admitted. “I spend a lot of time there as it is, so to spend more time now is really a daunting thought. But I did it, and it was super fun! The episode is amazing and I’m really glad that [recurring guest star and director] Debbie Allen pushed me to do it.”

Grey’s Anatomy
airs Thursdays at 8 p.m. ET/PT on ABC.

For more, watch the video below.