Jarring - appropriately termed. Compromise:
As DM, I will use the OOC and SAY formats. As a character, use the normal PbP procedures of the following:
Italicized = Thoughts of character
Quotes = Character Speech
Each character choose a color of text for the above two formats of speaking
As for the tattoo on Miranda, they actually requested that option. Miranda will know her limitation, and it only affects Fire based spells. She can still choose something besides fire and cold if the need arises. Although, with 7 characters, I am sure that you will find a way to deal with any threats that are immune to cold damage.