I’m driving my mother to her second week of radiation on a glorious spring day. Pale green leaf-lace froths on the trees, a verdant scribble working its way up the foothills of Mt. Greylock. Spring is an irrepressible fact in New England, not a cliché. And the weather is our favorite subject now that Mom has moderate Alzheimer’s.

Today, three horses graze in a newly lush pasture.

“Look!” she says.

“Yes,” I agree, adding: “Sometimes I still want to take riding lessons.”

“Me too!” she says, delighted.

“Let’s do it.”

We bask for a minute in the shared fantasy. Any coherent conversation is a gift, the verbal back-and-forth I once took for granted. How cross I used to get with her before the diagnosis, how frustrated with her anxiety, her chronic lateness, the myriad vexing habits I can’t even remember now. Why did it take first one illness, then another, for me to relax in her company?

Sunlight glimmers on the lake beside the hospital. Vast walls of windows offer patients a glimpse of water. One frail man sits in his wheelchair outside the double doors, parked in the sun. He is so thin he is nearly translucent and I make myself look him straight in the eye and say “Beautiful day,” as if he weren’t dying.

Radiation is tucked away in the basement. When the young nurse calls Mom for the appointment, she seems confused, looks back at me searchingly, but she goes with the woman while I sit on a couch with her caregiver. She needs 24/7 care in her home now, a rotating team of four, and Lisa’s on the day shift today. A recessed fish tank bubbles in the wall beside us; I wonder if the hospital design team has implemented recent studies that prove aquariums reduce stress and blood pressure. I try to watch the lazy angelfish drifting through coral décor but end up lost in my phone. When my mom returns, she’s not distressed. In fact, she’s smiling.

She’s in and out for 20-minute sessions, Monday through Friday for six weeks. What we dreaded seems doable now. The nurses are so kind; they care for Mom gently and graciously, without a touch of impatience. She’s doing well, says the radiologist. Better than expected, says the oncologist. Apparently squamous cell carcinoma is the best kind of cancer to get if you have to get anal cancer. It hasn’t spread and has a high cure rate and might just be a bump in the road, although the road we’re on is headed toward the desert of late-stage dementia.

At first I was shocked and furious about my mother’s diagnosis, believing that Alzheimer’s gave a person a free pass on other diseases. But aging is a high risk factor for cancer and Mom is nearly 71; if you do the math, it’s not uncommon to have dementia along with other illnesses that prevail among the elderly.

One of my brothers called her cancer “cruel and unusual punishment,” and we all braced for the suffering she’d endure. But anguish hasn’t come yet and maybe it never will; maybe the mercy of dementia is that it places Mom purely in the present moment, immune to fear and dread, to the psychological distress that often accompanies cancer treatment.

Don’t get me wrong, I’m not finding a silver lining. I never would have asked for this, would take it back if I could. My optimist father used to say that the Chinese character for “crisis” contained the word “opportunity,” but I’ve since learned that he was wrong. His entrepreneur’s mantra was a misinterpretation of language, a false New Age twist on Far Eastern wisdom, although it did offer me solace in times of despair.

And I can’t deny that something has changed for me, some guard let down, a window opened that allows me to love my mother like a cloudless sky.

Driving home, I play oldies radio and we sing along to “Here Comes the Sun.” Mom knows all the lyrics, belts them out in her sweet alto because Alzheimer’s doesn’t affect music memory, at least at this stage. Little darling, it’s been a long cold lonely winter. I wonder if it’s John or Paul on lead vocals. Later I look it up and learn it’s actually George who wrote and recorded the song, a fact Mom once would have known without Google, but all she knows now is music and spring wind and her oldest child in the driver’s seat singing it’s all right. Crooning the chorus, she is free of self-consciousness. She has cancer but she’s in a good mood.

My siblings and I had agonized about how to treat her carcinoma when she couldn’t understand what was happening to her own body. She’d been diagnosed with Alzheimer’s at age 68 and could no longer make a cup of tea, let alone any medical decisions. I’d consulted with her neurologist, fearing the aggressive chemo-radiotherapy might speed her cognitive decline (it probably wouldn’t, he told me). Because of the high cure rate and the excruciating consequences of letting her tumor grow, we went ahead with the recommended treatment. My brother was her health care proxy and made the decision we all believed she would have made for herself.

Before I leave, I embrace Mom in the kitchen. Every chance I get I hold her hand. I remember how I used to half-hug her with one arm, keeping my body stiff and apart, just the way my preteen daughter now deigns to hug me. I was protecting myself from the pressure of her love, a force that seemed to obliterate my selfhood. Now I can’t get enough.

My baby!” she says, pulling me closer.

“Your big baby,” I laugh. “Even my own babies are big now.”

“Well, that’s O.K.,” she answers. Sometimes she forgets I have children and what their names are, but she knows me, she’s happy to see me. Who else in my life has ever been so happy to see me walk through the door?

Last year the memory specialist tried to comfort us when we told him the Alzheimer’s was progressing rapidly. “When cognition falls away,” he said, “what remains is the ability to love and be loved.”