ML multiple machine upgrade question

Hi all, quick question...

I have upgraded my MBP to Mountain Lion through the Mac App store and had no problems. (so far)

I saved the ML installer to a DVD before running it.

My sister is entitled to a free upgrade to ML because she bought her Mac last week. Can I simply copy the installer from my DVD to her Apps folder and let her install it that way? Will it install with no hiccups?

Basically it seems silly to have to download the same 4gb of data AGAIN if it's just going to be exactly the same software, or is there something in the installer app that marks it as 'my' copy?

Thanks in advance!