clean install mac using other mac as proxy

What OS's are they running? Do you know what models they are?

If you are in the middle on nowhere with no OS disks what exactly are you going to 'clean install'? Your clone idea is a 'dirty install'.

It is not a good idea to clone one OS onto another especially when they are different models - iMacs have different drivers installed compared to a Macbook Pro. It may not boot.

Is the internet there capable of downloading 6GB or so to get the OS installer from the App store? You can clean install if they can support a downloadable OS.

Firewire may allow you to get data via target disk mode if they both have ports, but it depends on the state of the disk, if it is damaged it won't mount until it is fixed. Thunderbolt can do the same thing (the right leads allow you to mix & match).

How to use and troubleshoot FireWire target disk mode - Apple Support

Have you tried recovery mode to repair her disk with Disk Utility? It makes more sense to try diagnosing/ repairing it before trying reinstalls etc.

Sorry I thought the first post said her machine was an iMac.

The installer can be downloaded on your Macbook Pro & can be used to install onto her Macbook Pro. You do need to have 10.8 listed in your App Store account to download it. Sign in & confirm that please, Apple keep removing older OS's from sale which can make things awkward. You can use a tool to copy the OS installer onto a USB stick to make a bootable disk to install from, but you should try to repair her Mac first…

Can it boot into recovery mode?

OS X: About OS X Recovery - Apple Support

Hold cmd+r at startup, see if recovery mode starts up. She may not have a recovery partition, but give it a few attempts.

If recovery mode runs use Disk Utility to repair the disk, it may start booting if the disk is repaired.

See how that goes then post back & we can take it from there.