It could be her husband, Shining Armor. In the lore, they are in a relationship, so it's very likely that he would be the father. This would also bring in elements of their relationship and how they support each other during this time.
A possible plot is that an old enemy tries to take advantage of her pregnancy. Maybe they think she's vulnerable in this state. However, Princess Cadence proves them wrong by using her inner strength and the support of her friends and family. Also, there could be a plot about her sharing her pregnancy experiences with other female characters in the kingdom, creating a bond among them.
It could be her long - time boyfriend. They've been in a loving relationship for years, and this pregnancy is the next step in their journey together.
Perhaps it's a human boy who accidentally wandered into the fairy world. Tinkerbell, being curious, interacted with him, and in a magical turn of events, she became pregnant. This would create a lot of drama as the fairy world and the human world don't usually mix in such an intimate way, and there would be a struggle to figure out how to handle this situation.
It could be her long - time boyfriend. They might have been planning for a family in the future, but the pregnancy comes as a bit of a surprise earlier than expected.
Another possibility is that it's a result of some sort of experimental jutsu gone wrong. So there may not really be a traditional 'father' in the sense, but rather it's a consequence of Naruto's own actions in the world of ninja magic.
It could be her long - time boyfriend. They've been in a loving relationship, and this pregnancy is a natural step in their relationship journey.
It could be another hybrid like herself. Maybe there's a new character who is also part vampire and part human, and they fall in love and conceive a child.
It could be Flynn Rider. Since they have a strong relationship in the original story, it's very likely that he is the father. They are in love and have been through a lot together, so it would make sense for him to be the one.
It could be one of her close allies or friends. Maybe someone she has had a long - standing relationship with in the original story. For instance, if there is a character who has always been by her side and they share a deep emotional bond, he could be the father.
There's also the possibility that it was an accident involving a time - traveling character. Perhaps someone from the future came back in time and accidentally caused Frieza's pregnancy through some unforeseen interaction. This would open up a whole can of worms in terms of time - travel paradoxes and how it affects the future of the 'Dragon Ball' universe.