I don't know why anyone hasn't pointed it out, but that's absolutely genius that she started from a spark. Honestly, it makes perfect sense! Two fire people make "friction" which makes "sparks" eventually, and the spark attaches to a candle and becomes a fire baby! That would explain why people keep candles in the bedroom, too.
I had a theory of the Fire Count being the Flame King's brother. Flame King killed him along with his wife because she was protecting his brother. And that's why we won't see FP's mother. And I also made it so that FP witnessed the death of her mother, causing her current mood swings.
"And then Rapunzel found she actually liked being held captive for all eternity. The End" "Dad, you've been changing the endings to stories a lot lately...is there something you want to tell me?" "Um...maaaaybe..."