(This may offend all Flame Princess fans but this is just mine and my cousins opinions)
Some may be valid some may be not ? Either way their just our opinions.
1) What if she becomes unstable again?
I mean remember in "Burning Low" Pb said "She's
stablelized were safe for now" get that "For NOW"
that does not mean forever.
2) She's made of FIRE!
I mean its kind of a hastle to keep putting tinfoil or flame shield on finn. I mean any time the flame shield could were off or the tinfoil could rip. And she could burn finn without even trying.
3) She sometimes can't control her powers.
I mean remember in "Vault of Bones" she couldent control them she just kept burning away. Remember she said the The Power of DISTRUTION!!! (come on!!!) she spun out of control!
4)She may not have the same taste with finn. Remember in "Vault of Bones she didnt like finn's way . (HERE) "Finn im not having any fun
i dont like doing things your way." see what i mean.