Her behavior is not unusual, say psychologists who help grieving spouses. In fact, it is normal -- a kind of "magical thinking."
Joan Didion coined the term in her 2005 memoir, "The Year of Magical Thinking," about the death of her husband John Gregory Dunne.
In the days after Dunne collapsed of a heart attack before her at dinner, Didion wrote she was afraid to give away his shoes, for fear that he would return and need them.
Vicki Kennedy, the widow of Sen. Ted Kennedy, who died of brain cancer a year ago, said his absence in their Washington home is palpable: "Teddy's in every room."
"My heart is so heavy," she recently told the Boston Globe.
Those who grieve live "in a different world," according to Maryland psychologist Ursula Weide, a bereavement specialist.
"And there are no meds to 'treat' the trauma," she said. "Society wants an instant fix but there is none."
Niemi, who will appear on the televised Stand UpTo Cancer benefit today to raise funds for research, said she always texted Swayze while traveling.
"I just put what I always did: 'I love you.' And then I cried for a little bit to myself," she told People magazine. "It [the text message] didn't come back. So either somewhere out there received it, or someone's going, 'Somebody loves me!' And you know what? I figured it was a win-win situation."
Grief has no timeline, according to psychological experts, and it varies according to each individual. According to Weide, about 15 percent of those with a loss experience "traumatic grief," unable to move forward.
The sense of loss is "permanent," and the person who feels it is forever changed, she said, but most are eventually able to move on from the acute phase and manage the pain.
Weide knows. She lost her husband at the age of 47.
"When I received the phone call, I was pushed into a dimension of existence I had been unaware of so far," she writes on her website. "I was unable to eat or sleep for three days and nights, running on something unknown inside of me. Once fitful sleep returned for a few hours each night, I fought waking up in the morning, knowing that something dreadful was going to overwhelm me once I would become fully conscious. During my waking hours, I felt locked into a concrete cell of pain which I was unable to escape. Only death would provide relief, as I knew."
Weide describes being "amnesic," forgetting words mid-sentence and getting lost driving, living her life like a robot in slow motion. She had no appetite and chronic stomach pain.
She likens "traumatic grief" to post-traumatic stress syndrome and major depression and advocates for treating it as such.
Kind words and comforting phrases are not enough. Many who are experiencing traumatic grief need to treat "dimensions of pain and trauma we are unable to gauge unless we have been there ourselves, " said Weide.
"We do not control grief, it controls us," she said. "You cannot push a person to focus on the future or stop tweeting or throw away the shoes. But we eventually learn to live with it. The grief changes over time. We develop coping skills to fully function again, but it's different from before."
Dr. Katherine Shear, professor of psychiatry in social work at Columbia University, has been a pioneer in studies and treatment of grief.
In 2005, she published the first randomized controlled treatment study for complicated grief, grief that is unresolved and disabling.
"Grief is permanent," she said, but it changes over time.
Grief associated with the loss of a spouse can be "heightened" because of the "every-day-life-ness" and caregiving nature of the relationship.
For most, acute grief is a "very dramatic" experience with unique thoughts, feelings and behaviors, according to Shear.
Intense yearning for the lost spouse is intermixed with sadness. Sometimes it can alternate, even a few weeks after the death, with postive feelings.
"It's a very emotional state that is generally unfamiliar to people," she said. 'One of the typical things that happens is almost a confusion about whether the person is there or not. The idea that they are sitting in the room or a strong expectation that the doorbell will ring and the person will come. Or they will wake up from a dream and he will be there."
Sometimes those who are grieving actually see or hear the other person who died, according to Shear.
"This is perfectly natural and not a cause for alarm," she said. "We can hallucinate during grief."
Another common behavior is to avoid any reminders of the person. "You want to damp down and get control of the emotions in some way," she said.
Anniversaries of a loved one's death can be particularly difficult. "It's a very natural and unavoidable trigger," said Shear. "You can drive down a different street that reminds you of the person, but you cannot escape the day he died."
By the end of the first year, though grief is not over, people generally start to come to terms with the loss of a loved one.
"And then all of a sudden they can be thrown back to feelings they have not had for months and they can be surprised," she said.
That may have been the case with Lisa Nieme as the one-year anniversary of Swayze's death approached. But she told People magazine she is slowly coming to terms with her "overwhelming" loss.
"I know he wanted me to be okay, and I am stronger now," Nieme said. "The fact that I've had some good days definitely gives me hope that I can have more."
As for texting, Shear said it's just another way "to feel closer to that person." Others might embrace a spouse's clothing, or look at a favorite picture or belongings.
"Texting is like talking to people who die," she said. "It may be the most modern way of manifesting a journal. [Lisa Niemi] may know her husband won't get this. But I see this as a kind of compulsion of sorts to get closer to him."
"A person reaches out to look for connections in a range of different ways," said Shear. "It's not odd. It's just like looking at a picture album of a vacation they loved."