Rinali was with them for few years and they didn't noticed that her innocence is kinda different than others :)
THEORY 3.11 : Clock sword. Creates a sword from one of clocks arm - but it isn't used to direct combat. This sword can change its size, lenght or... place (like his top appearing on the back of enemy).
They don't know what the Heart is like at all. It's a total mystery. Besides, it doesn't look like she had any idea that it was weird, either - so it was obviously a very sneaky Innocence.
...sword? Isn't that a violation of Kanda's rights as the lone swordsman in the series?
If exorcist doesn't understand his innocence, no one will - probably innocence reacts to partners psyche - if someone wants to fight, he will get offensive innocence (Kanda and Mugen or Crowley and his teeth), if someone wants to protect, he will get a innocence which can act like a shield and weapon (Allen) or agile which makes you able to protect others with your high-speed reactions (Rinali). Since Allen's innocence and character changed a little, his innocence changed too (Allen accepted that it is neccesary to kill sometimes).
Crowley innocence changed a little when he decided to protect (blood becoming an armour or becoming a bloody-guardian).
If Miranda chose to fight and not just support, I think her innocence could change too.
THEORY 12.07.1987 : Time forward - Make things faster, which might overheat things or exhaust them (since the speed will be to great for their bodies and minds to comprehend).
Sometimes it takes time and experience for an Exorcist to learn about his/her Innocence - remember the China training arc where Allen couldn't do anything? He gets it *now*. Rinari's Innocence is doing weird things, and it'll probably mean that she'll learn to understand it in the future.
(Allen always killed things - and all I can see Rinari's Innocence doing is, um, fighting. She'll probably end up protecting things more, though.)
It doesn't seem to be in Miranda's personality to fight. Even in the Rewinding Town, she was purely used for support. Anyway, there are enough Exorcists that can fight, and hers is really useful as it is, so everything works out.
I kinda can easily see Miranda getting pissed of and then "magically" learn something new about her innocence.
Some Noah : Your friends are weak, they just using you and doesn't care about you. Your just slowing them down
Miranda : No ! I trust them bla bla bla, I know they don't think like that - your wrong bla bla bla
Noah : Bla bla bla - Your friends are two faced and liars
Miranda :TAKE THAT BACK YOU SON OF A bla bla bla
"bla bla bla" - fit some lame verses used all the time in shounen manga's or in movie "300".
...that seems like something Rinari would do, not Miranda. o_o Miranda would probably just become depressed and a dark cloud comes and kills the akuma. XD
Edit: YES! 300 insults! =D
i think miranda would throw her disc and use a time thing to make it move a whole lot faster than how fast she can throw it using her physical strength, then it would cut thru akuma :)
That doesn't have to do with her time-possessing-and-manipulating Innocence-power in any way, so this 'using-disk-as-sorta-missile' isn't really working...........but it would be for sure a more active way to fight....
Maybe she won't use time as a weapon, though - every other equipment type has taken a shape that is a weapon itself, and can be used as one, despite its other powers. Rabi uses a hammer with elemental seals, but he's used it as a hammer too - and who knows all the things Rinari's boots could do besides, um, kick things (???).
Hmm... the only reason why Miranda has yet to learn an actual attack is because it's not as obvious as all the other weapons. However... I'd think that experiencing a whole bunch of injuries all at once would be a lot worse than sustaining separate injuries one at a time. >_>
The most obvious method is speeding up oneself to the point of appearing invisible to your enemies. Another less obvious method is creating small pockets of time to alter the battlefield to your advantage. If Miranda gains enough control over her abilities, she may be able to use bubble-like attacks in order to trap and destroy Akuma. So... yeah... bubbles of time. That's her attack. >_>