Need help with macro

[Sanvich]

I would like my friend's Death Knight to cast Deathchill then Frost Strike but I want the icon to only be lit up when Frost Strike is available.

Currently I have

/castsequence Deathchill
/castsequence Frost Strike

It works, but it's always lit up since Deathchill doesnt cost 40 Runic Power, and since she's new to the game, I wanted to find a way to simplify it like, "Dont push unless lit."

Thanks.

[Seerah]

#show Frost Strike
/castsequence Deathchill, Frost Strike

edit: this requires two key presses. If Deathchill does not trigger the global cooldown, then you can do this:
#show Frost Strike
/cast Deathchill
/cast Frost Strike