I am concerned you would only get yourself killed. 

Well, if it turns out I can't go home, that's how I get myself a successor.

I do not think that is at all wise, child.

It's hardly my first choice.

All right. The Valar cannot send you back?

Ulmo suggested I go to Valinor for closer inspection. It's weeks of hiking even for people who can reliably balance on ice, which I can't - I'm not sure I could make the trip at all, and my brother might freeze while I slept, if we didn't bring people with us, it would be a major production - and he said he'd tell the other Valar that I'm in a hurry and they'd get back to me, which might mean they can't do it but might not.

I am sorry. Thus the urgency of your mission to learn whether you can aid us in the war effort?

Better to know sooner than later.

She stands. Let us go outside. And her body splits - into one with the same appearance, which sits back down, and one with a brittler more metallic appearance who walks towards Kiri. 

Kiri shoos Aleko to go stand near Maitimo and wait in case there's some kind of splash effect, and she follows Melian.

And they go to a spacious field outside Menegroth and far from everyone. This form should be very hard to bother, she says, and absorb lots of energy if destroyed.  I can do a better one if it seems not to be working well. 

Preference for starting with heat or cold?

None at all. 

Cold first, then, probably less chance of explosions. Cold cold cold colder colder colder.

No problems, up until the point where being that cold would make movement impossible, and then she can expend some energy to move despite the cold. 

Does that warm her up or just work around it?

Just works around it, looks like. 

Hmmm.

Kiri starts going colder, faster.

Still moving, though very sluggishly. 

I can project the internal experience if that'd be useful to you? 

It might? But I haven't actually felt personally cold in years so not too vividly please.

Oh, this form doesn't have nerve endings, they're hard to do and wouldn't be very useful. What's interesting is how it interacts with my magic -

And she sends. The world around her body is under her absolute control, ordinarily, but now it is very slowly so - the ordinary avenues for exertion don't work, she has to push things oddly, and there's resistance - it takes more of her attention...

I think I can go colder. Should I stop here or try it?

Do keep going.

Fëanáro mentioned a temperature at which things stopped - moving - altogether - which means that until that happens there must be more heat there to siphon away -

If so, it's not siphoning. She's still moving, with effort.