Itinerary 6-8 weeks

There will be a lot of other backpackers - if you want to be with them, just stick to the tourist trail. Maybe something like starting in Yogyakarta in Java, then traveling through Bali, Lombok and Flores would suit you, with the partying to be done in Kuta, Bali, and on Gili Trawangan off Lombok.
If you find you have extra time left, add Sulawesi.

Be aware that you can get a 1-month free visa (Visa On Arrival), but if you intend to stay two months you'll need to get a visa for that period. Otherwise you'll have to leave the country before your short-visa ends and return.

While getting a 60 day visa back home is preferable, she can also pay for an extendable 30 days long visa on arrival at most entry points, and extend that by another 30 days within the country.

Another plus for the itinerary suggested by Laszlo: its very varied, in terms of culture / religion and nature. Java and Lombok are mostly muslim, Bali has a very interesting and rich hindu culture, and Flores is mostly catholic. And you have beautiful nature every where, places to party on Bali, snorkelling off Flores, Lombok and Bali. And culture everywhere.

Trying to extend a visa-on-arrival can be a lot of hassle.

"can be" true and there are places best avoided but not always. True I would if at all possible get the 60 day visa beforehand if I could

As for where to go well I would read up a bit first because you need to narrow things down a bit if you are going to get sensible help on this

Come on @bigal1 , at least @Ashley90 has told us her interests!
That's already much more than most clueless people asking for advice on TT about where to go do.
But of course she should also get and read a guidebook, something ever fewer people seem to do.

true point taken

However Indonesia is such a big country offering such variation that it is hard to know where to begin and how much they wish to travel in that time.

They could for instance start in medan and head through java and on to Bali or start in Maumere and work back to Bali within that time frame and experience everything but they would be very different experiences

Hai Ashley,

I'm putra come from indonesia, and i live in Bali, if you want travel to indonesia, i suggest first trip come to Bali, So many backpackers from all over in the world come to bali and then they maybe will share with you how Indonesia look like, then you can make decisions where you want to go.

My idea is come to Bali first and after that you can come to lombok or another island close by Bali, also from bali you can take bus going to Java, the final in Jakarta. Jakarta have many nice Island also even the busy city, if you are first time come to indonesia, i suggest come to that place, because the other place have different culture and different attitude and you need to know exactly where you want to go and make decisions.