Dee was Born in Tall Tale beyond the Unicorn Ranges. She left home to see more of Equestria and gain some independence. She eventually settled in Ponyville and has remained there since.
Personality
Dee is a quiet pony at heart and not confident in herself or her abilities. She loves to talk to other ponies and really puts herself out there to converse to ponies and make them feel loved and important. This is special to her as she struggled to fit in when she was young. Thus she put on a rebellious personality which only increased her loneliness and caused her to get into trouble.
Kindness is special to her. It is the core of her personality and will occasionally make her show more courage than she thinks she can show. She is still uncertain of herself and afraid of being rejected but will put herself out there for other ponies as she knows how it feels.
She does not like arrogance and pride and ponies that are unkind or dismissive. If she encounters these ponies she will be kind to them, but not reveal any of her real self.
She loves to meet kind ponies, ponies that are willing to talk not only about themselves but are also interested in others. It is with these ponies that Dee will open up with and trust. But it does take time for her to trust.
Cutie Mark
Cutie Mark
Her Cutie Mark is that of two dolphins swimming around each other. The dolphins represent the joy and freedom that many ponies feel about the creatures and the attachment they have to dreams. The colours of the dolphins are natural taken from the ocean and the forest.
Background
Because of Dee's lack of confidence, she put on a rebellious pony attitude when she was younger. Dee made friends by fitting into a rebellious crowd and pretending to be someone she wasn't. She changed her mane and attitude to fit in as the picture shows.
Dee in her younger days.
Her immaturity and choice of friends resulted in her getting into trouble and being influenced by other ponies easily. She trusted without question and just wanted to have fun when she was young. Unfortunately during a midnight swim at the ocean with some of her friends, Dee was swept out to sea. Her "friends" left her and headed back to shore. As she sunk into the water the last thing she remembered was reaching out to the water and animals around her with her magic. She saw her horn glow a brilliant aqua and dolphins swimming around her before she blacked out. She woke up on the shore with her cutie mark.
Since then she has had an affinity with water and with animals, particularly sea creatures. She has also realised the transience of pretending to be some pony you are not. She left Tall Tail and all her friends and arrived in Ponyville feeling the most afraid and uncertain she had ever felt. She has a diary of her feelings and ponies she has met since she arrived in Ponyville.
Ponyville
Since arriving in Ponyville Dee has made many friends and had many interests. She has opened up a Art shop. Unfortunately it burned down. She has now opened up a Paint and Tea Shop. It sells Magic Paint and Tea. Dee loves tea and in particular loves having tea with friends and chatting. She also has an affinity for adventure and though she is not skilled she loves going on an adventure with a friend.
In her time in Ponyville, She received a riddle which took her over a year to solve and sent her on many adventures. It taught her about a greater gift and quality. Dee wrote these aspects and discoveries in her journal.
Dee loved attending the Gala. She enjoys dressing in beautiful clothes as they make her feel special. Sometimes she will find an excuse to wear a beautiful dress out. She likes going to gatherings and parties mainly to talk to ponies and see them enjoying themselves.
Explorers Guild
Dee is now a member of the Explorers Guild and will occasionally stay there in one of the rooms. She met with Aurora White and upon her completion of a difficult riddle given to her she would be accepted as part of the Guild.
It took her over a year to solve the riddle it taught her a beautiful lesson. She has catalogued her journey among other things in her Diary since she arrived in Ponyville.
Now Dee often and unintentionally gets lost in the secret passages and back doors of the Guild.
Canterlot
Although Dee lives in Ponyville, she often visits Canterlot to fulfil her duties as a Night Maid of Princess Luna. She stays at the Castle in her quarters or she will stay with Stormchaser , Princess Luna's head maid.
https://twitter.com/mlp_Luna/status/549335260916629504
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Staying with Stormchaser led to many adventures and Dee considers her one of her closest friends. She has shared many good times with Stormy, in particular the time a number of them dressed up in Sailor Moon Pony outfits for Halloween! She keeps her "Jupiter" Sailor Moon Pony Costume ready to go in her closet!
Dee's Journal
Dee Keeps a diary of her thoughts and feelings since she has been here in Ponyville.
It is quite long but you can read through it here.