These are characters who are princesses, but aren't official members of the Disney Princess franchise. They sometimes or rarely are included in some products. Some unofficials aren't included at all due to it's marketing and how successful their movies where. There were some like Esmeralda, Jane Porter and Tinkerbell were in the franchise and later removed to due money issues and Tinker Bell now has her own franchise called "Disney Fairies."
Reasons why they aren't included:
Patty (The Cookie Queen) From The Cookie Carnival - She's not an official disney princess because she's a cookie, meaning not a human. She's also not in the official line-up because she was one of the two main characters in a animated short on the small screen (TV)
Persephone (The Goddess of Spring) - She's not in the official line-up because she was one of the two main characters in a animated short on the small screen (TV)
Minnie Mouse - She is sometimes depicted as a princess in some cartoon shorts, however is not included because she is not human and also is part of several other franchises of Mickey Mouse.
Daisy Duck - Like Minnie, she's not human and is included in several Mickey Mouse franchises
Faline from Bambi - She is not official Disney Princess because she is not human
Alice from Alice in Wonderland - She is not an official member of the Disney Princesses because, in spite of her act of heroism, she isn't royalty.
Wendy from Peter Pan - She is not part of the Disney Princesses because she is not old enough and is not royalty nor she has act of heroism
Tinker Bell from Peter Pan - She was removed from the franchise because she now has her own franchise called Disney Fairies. She is not human, though she is human-like. She was never actually royal, and was included for her acts of heroism, similar to Mulan.
Shanti from The Jungle Book - She is not an official Disney Princess for unknown reasons.
Maid Marian from Robin Hood - She is not an official member of the Disney Princess Franchise because she is non human
Princess Eilonwy from The Black Cauldron - She is not an official member of the Disney Princess franchise because of it being seen as lackluster and also because of the film done extremely negatively in the box office.
Nala from The Lion King - She is not an official Disney Princess because she is not human
Esmeralda from The Hunchback of Notre Dame - She was removed from the franchise for unknown reasons. She was never royal, but was included for her heroism and compassion, similar to Mulan.
Megara from Hercules - She is not part of the Disney Princesses because her film was generally viewed as lackluster, although the movie was successful in the box office, it may have lot of negative reviews.
Jane Porter from Tarzan - She was once considered for the franchise, but ultimately never joined for unknown reasons in spite of Tarzan as The King of The Jungle, making her the Queen of The Jungle as well as of being his wife, which is not the reason why she isn't included with the Disney Princesses.
Kiara from The Lion King II: Simba's Pride - She is not included because she is not human and was introduced into a sequel
Princess Melody from The Little Mermaid 2: Return to the Sea - She is not an official member of the Disney Princesses because she was introduced into a sequel
Jessie from Toy Story 2 - She is not an official member of the Disney Princess Franchise because she is not human, not royalty and was introduced into a sequel.
Kida from Atlantis: The Lost Empire - She is not included because her film was a box office bomb.
Vanellope von Schweetz from Wreck-It Ralph - She is not included because she rejected her noble title in favor of being President of Sugar Rush, and for her royal status being a spoiler for her film.
Princess Anna and Queen Elsa from Frozen - They were suppose to join the Disney Princess lineup as 12th and 13th Disney Princesses, however since their franchise is so sucessfull due to the movie made 1.2 billion in the box office, they were ended up not included because they would effectivly overshadow the other members of the franchise, meaning Disney would have to remove all of the official members and Anna and Elsa would be the only ones standing in the Disney Princess lineup which is something that Disney would definitley never want to happen, so they currently have their own franchise. However, they'll probably join eventually since they were confirmed to be in Ralph Breaks the Internet along with the other princesses, especially Moana.
Princess Sofia from Sofia The First - She is not an official member of the Disney Princess franchise because she is from a television series, also Disney stated also why because she is too young to be considered an Official Disney Princess.
Princess Elena from Elena from Avalor - She is not an official Disney Princess because she is from a television series. She would only join if she gets a movie being released in the theaters.
Moana from Moana. She is not an official Disney Princess yet, although Maui says that she is. However, she could still join the franchise at a future time.
There are a bunch of other heroines, but aren't considered Disney Princesses at all mostly because their from Disney Television Animation which does not meet the criteria of considering a character an Disney Princess whether or not official or unofficial.