Prologues, pro or con?

I've read lots of debates about prologues on different literary sites. I don't have strong feelings either way, and have never been bummed out or felt led astray by a prologue. Children of the Waters is only my 2nd novel, so I'm no expert, but for this book it felt right to me to have a prologue. This prologue hints at what the story is about and is from the POV of someone we only hear from again once later in the book when the letter she writes in the prologue is read. I think it works because the prologue, even though from her POV, isn't really so much about her. And the first main character we hear from after the prologue is the granddaughter, Trish, she writes to in the prologue.

What do you all think? Prologues, for them or against them? What do you think makes a good one?

And as a little taste, here's my uncorrected, unedited prologue:

Time was short. Maxine Kuepper was starting to say things she didn’t mean. Yesterday, she told her granddaughter to Move my dish, when she wanted to ask her to bend her leg. Trish stared, stumped and afraid, yet all Maxine could do was yell the word “dish” over and over knowing that she wasn’t making any sense.

Cell by cell, bone by bone, Maxine was floating away. She didn’t know if it was the cancer or the medication that made her say such things. She was wearing a patch that released heavy doses of relief into her bloodstream, and still the littlest weight on her, like a sheet or the cotton nightgowns they dressed her in, hurt. The nurse promised that when the time came Maxine wouldn’t have any pain. “We’ll snow you out,” the nurse assured her. “Don’t worry.”

Maxine would die the way her daughter did: like a mermaid swimming at the bottom of an ocean of drugs. It was small comfort after all these years to believe that Jocelyn hadn’t been in any pain when she died. Jocelyn. Such a cultivated name for a daughter who would not be tamed.

They were coming for her, Jocelyn and John, her husband, both dead. She dreamed of them so much now that sometimes she could swear they were really here in this room, whispering their secrets to her. They were coming for her. If they weren’t already here, she knew they were just over the other side waiting. And even though she was only sixty years old and her granddaughter Trish was only seventeen, she was ready to join them. But she had one last thing she had to do. She had secrets of her own to tell.

She looked at the Polaroid picture she’d kept hidden for thirteen years. Not even John knew she had proof of this moment. There was Jocelyn, blond and movie-star gorgeous even after just giving birth, holding the baby, only hours old with a cap of thick dark hair. And Trish, smiling wide, skin, teeth and hair white as cream, on the hospital bed next to them. Both girls marked with a stain that couldn’t be washed away.

Maxine wished she had done things differently. But wishes are for the living. She sighed and pain rippled through her as her lungs pushed up against the battlefield of her ribs and the space where her left breast used to be. She raised the pen with the same amount of exertion that it used to take to lift a gallon of milk and began to write.

The nurse said don’t worry. But how could she not? What would they think of her? Would they hate her or would they be glad to know the truth? Probably both. But she would do this one last thing for them. She would make things right. As soon as Trish came home, Maxine would give her the letter.

I should have told you this a long time ago, she wrote to her granddaughter, putting everything that was in her battered heart onto the page so that when the time came cowardice wouldn’t seal her lips. Each word, a lifetime.

Just as she finished, she heard the front door open and close. Or she thought she did. Lately it was hard to tell what sounds were real and what sounds were memories sweeping over her like ocean waves. But if it was Trish coming in, Maxine knew she did not have the strength to see the look on her granddaughter’s face after she read this letter. She didn’t have the strength to answer the question she knew would come no matter how hard she tried to explain: How could you?

She opened the box, put the letter and photo inside, and replaced the lid. After she was gone, Trish would find everything she needed to know. When Maxine was buried, her lies would be unearthed. It wouldn’t be long now. She was sipping life from a glass that was neither half empty, nor half full, a glass emptying so rapidly she could see it in the eyes of the hospice nurses and the few friends who came to visit her at home.

The bedroom door opened, and Trish poked her head in. “Nana, you awake?”
Maxine nodded, thinking For now, and, Please God let them forgive me.