Queen Elizabeth II has faced one of the most difficult years of her life.

In April, she lost her husband of 73 years, Prince Philip, just short of his 100th birthday. Her second son Prince Andrew is still facing legal woes even after exiting public life over his controversial friendship with convicted sex offender Jeffrey Epstein. And her grandson, Prince Harry, allegedly still has a strained relationship with the British royal family after he and his wife, Meghan Markle, stepped back as senior members.

And then in the late fall, the reigning monarch, 95, had several health setbacks, which stirred headlines. She has since been largely confined to Windsor Castle.

In the latest issue of PEOPLE Royals, out on Friday, the queen’s biographer Ingrid Seward told the outlet that "her ability to compartmentalize has been extremely helpful in her life" as she balances both her personal and public life.

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Queen Elizabeth

Queen Elizabeth II was seen using a cane in October. (Arthur Edwards/Pool Photo via AP)

"Fundamentally she puts things in a box and says ‘that can be dealt with on Thursday,’ for example," Seward explained. "She won't let things crowd in on her. She is mentally disciplined and that has helped her through these 70 years. It has enabled her to deal with all the things and not allow things to overwhelm her. It goes a long way towards explaining her ability to be able to still be working at this age."

Elizabeth is expected to be surrounded by her family during Christmas at Sandringham House in Norfolk. According to the outlet, she will stay there until after the anniversary of the February 6th death of her father, King George VI. It will be the first time in 73 years without Philip by her side.

"She will be missing his companionship deeply," a palace insider told the outlet. "But she is a very stoic person."

Another source told the outlet that her "religious faith" has been essential during such tough times.

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Prince Philip

In this Aug. 1951 file photo, Britain's Queen Elizabeth II, then Princess Elizabeth, stands with her husband Prince Philip, the Duke of Edinburgh, and their children Prince Charles and Princess Anne at Clarence House, the royal couple's London residence. Prince Philip was born into the Greek royal family but spent almost all of his life as a pillar of the British one. His path was forged when he married the heir to the British throne, and a promising naval career was cut short when his wife suddenly became Queen Elizabeth II. Nevertheless, he set about forging a place for himself as royal consort. He was a patron of charities and a supporter of projects for young people. He was married for more than 73 years and was still carrying out royal engagements into his late 90s. (AP Photo/Eddie Worth)

"It feels to me, she can carry on for some time," the insider added.

Back in October, royal author Matthew Dennison told Fox News that the queen has been turning to her Christian faith to overcome the ongoing drama rocking the palace.

"She has a strong religious faith," he shared. "One of the things that the queen has done is pray throughout all of this. She also has a loyal, supportive group of private secretaries, ladies in waiting and devoted friends who have been a strong system around her. She also has the support of her close-knit family."

"She finds it difficult to confront difficult issues," he noted. "I think she has gotten better over time."

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Queen Elizabeth II visits the Coronation Street set

Queen Elizabeth II is expected to be with the rest of the royals on Christmas. (AP/Scott Heppell)

Dennison, who has written eight critically acclaimed books, has recently penned "The Queen," a new biography that explores Elizabeth’s decades-long reign. He spoke to several palace insiders, both past and present, to tell the queen’s story. Dennison said that during his research, faith played a prominent role in the royal’s life.

"She has a connection with the divine," he explained. "She is a monarch who made a promise before God to fulfill her duty. And it’s a promise she has taken very seriously in her life. Even as a young woman, she has faced an overwhelming expectation on what kind of queen she should be… She has embraced that role."

Despite losing her beloved husband, Dennison said Elizabeth has zero plans to step down. Her eldest son Prince Charles, 73, is first in line to the throne.

"There wasn’t ever a realistic expectation that the death of the Duke of Edinburgh would lead the queen to abdicate," Dennison shared. "In the very few times she has spoken about it to her close friends, she has always been quite clear that the promises she made in her coronation are binding. These are promises she made to God in the church. These are holy promises. She’s always said she would abdicate only if she got Alzheimer’s disease, a stroke, or something that would leave her incapacitated in some way. But this role is for life."