AFAIK no such site exists. But it's not too arduous to compare your options. I'm an Australian living in New York and I accumulate all my miles with SPG so this is a question I'm often faced with. If you transfer SPG points to AA for travel on QF, the redemption chart is here. I avoid DL simply because I find it so frustrating to navigate their "Low", "Medium" and "High" award bands. For travel on United or on Air Canada via YVR (or another Star Alliance carrier) you'd probably be best to use Mileage Plus, whose chart is here (incidentally, I found this simply by googling "united mileage plus partner award chart".)

In my experience, especially with 12 months' notice, I'd opt for flying with Qantas via the AAdvantage program. Despite its comparatively poor J/F availability, you'll be fine if you sign up for an expertflyer account for ten bucks a month and set availability alerts. If I were you I'd book seats in economy class as a backup, and then nab J/F seats as they open up. No guarantee the whole party can travel together in First but, across a few flights and classes, you'll find something good enough. There are 8 Qantas flights a day between the US and Oz/NZ (JFK-SYD, DFW-BNE, DFW-SYD, LAX-MEL, LAX-BNE, LAX-AKL, 2xLAX-MEL, 2xLAX-SYD) and although several of those are in fact different sectors of the same flight, it's wise to set alerts for all of them as the award availability differs on each. The other benefits of using QF & AA are that the surcharges and taxes are miniscule, and the First Class lounges in Sydney and Melbourne (if she scores an F seat on the return) are absolutely outstanding -- free spa/massages, free five-star restaurant, etc. Hope she has a great trip.