It was obvious when Clarissa was four weeks old that she and Granny Denise would be best friends.
Clarissa started to sleep at Granny's on Friday nights so her mum and dad could have a date night. Since then, the pair have spent the school holidays together and go on trips to Cornwall.
So when Denise started to feel depressed after developing an aneurysm in her brain, Clarissa, who is now four, really noticed. And she took matters into her own hands.
"She decided to do something special to cheer up Granny," Clarissa's mum, Felicity Greenfield, who is 23 and lives in Derbyshire, says.
"Clarissa has a lot of special memories with my mum and cares very deeply for her. There hasn't been a day in Clarissa's life when they haven't spoken.
"She wanted to get letters from places they'd been together and places that Granny wanted to go.
"My mum loves it at Land's End, in Cornwall, so Clarissa asked if we can get a message from the pirates there."
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Clarissa and Felicity planned to make a scrapbook with the letters to give to Denise on her 52nd birthday, in March.
Felicity put a call out on Facebook at the end of January. Together they waited to see what would happen.
Hong Kong, China, United States, Australia - the messages poured in from around the world. In the first week, Clarissa and Felicity received more than 160 letters.
Derby County footballers and famous attractions also sent notes, including the Shard in London and Clarissa's favourite, the donkey sanctuary in Cornwall.
"'Are there any more letters?" Clarissa keeps asking, Felicity says, adding: "What started off as a silly idea really has now become this big thing."
"I think people want to get involved because it's from a little girl to her Granny."
"We're really hopeful that this will cheer her up - since her first aneurysm, in 2015, her health has been deteriorating.
"She's lost some mobility and can't do the same things anymore."
Now, the total has reached 207 letters.
Keeping the mission secret became difficult when the Facebook call quickly spread, but Denise still doesn't know the full extent of what her granddaughter has managed to do.
"I'm not allowed to see all the messages, so the final scrapbook will be a surprise," Denise says.
"As a granny and a mum, you always think what you're doing is normal - so it's nice to see how loving Clarissa is."
"I'm really proud of her."
Denise says: "With my illness, I just try to get on the best I can - but it is what it is."
And realising that strangers around the world had sent messages was "amazing".
She says: "It's lovely to see that people are taking time out of their lives.
"You just think everyone is so wrapped in their own world and things can be very gloomy, so this really puts a smile on my face.
"I'll always treasure it, and it will be one of Clarissa's memories in the future."
By Georgina Rannard, UGC & Social news