"Last year we got her a present and she just kept opening it over and over again," says 16-year-old Charlotte.

"She was happy but she wasn't really aware of why she'd got it and now she's in a worse state than she was last year."

Charlotte is telling Newsbeat about her grandma, who has dementia and now lives in a care home full-time.

She says her grandma came to visit her family on Christmas Day but got "quite distressed".

This year, she says, they will go to the nursing home to visit her instead.

"It is really sad because we used to spend most of Christmas with her and my granddad before he died," she explains.

"It's really difficult because it's so different. There's only me, my mum and dad - I don't have any siblings.

"It feels sort of empty in a way, because all the family aren't here. It's not filled with joy, which is what Christmas should be all about."

She's not there mentally. She doesn't even know my name Charlotte

There are around 850,000 people living with a dementia diagnosis in the UK. The most common form is Alzheimer's disease, which is what Charlotte's grandma has.

New research from the Alzheimer's Society suggests that more than half of those affected find Christmas to be the most isolating time of year.

People with dementia "might not recognise" that it is Christmas, says Kathryn Smith from the charity, but the holidays can be distressing, especially if routines are disrupted.

"There's a lot more noise, a lot of lights, a lot more people around," she explains.

It feels sort of empty in a way, because all the family aren't here Charlotte

But it's not just those who have the condition themselves who can struggle.

"I think the families can quite often feel guilty or sad because they know things are not what they used to be with their loved ones," says Charlotte.

"It'd be nice if people were more aware of how it affects the family as well as the person with dementia.

"She's not there mentally. She doesn't even know my name.

"She knows I'm something to do with her but she wouldn't know I was her granddaughter or anything like that, which is just really difficult."

Charlotte's grandma is called Frances and she's 84.

"She used to be a dinner lady when she was younger," she says.

"She's always been a really family person. She has two daughters - my mum and her sister."

Every year Frances would make special handmade Christmas cards. Not receiving one of those is something Charlotte notices.

I think the families can quite often feel guilty or sad because they know things are not what they used to be with their loved ones Kathryn Smith Alzheimer's Society

As well as visiting her in the care home, Charlotte and her family will make sure to keep Frances at the forefront of the Christmas celebrations this year.

"My mum will probably buy me a present on my nanna's behalf, so it'll be something my nanna would have bought me if she was OK, which will be lovely to open," says Charlotte.

"My parents work a lot over Christmas normally, however they've both got Christmas off this year, which is really nice.

"Spending it with them will make it a lot happier for me."

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