Whether she wants to or not, I don't think she'll be able to fit all three kids without keeping at least one of the twins rear-facing. I think she needs a Radian for each of the twins and experiment to see what works best: Nautilus - RF Radian - FF Radian or RF Radian - Nautilus - RF Radian. She may need a Radian for the 3 year old, too. I know I wouldn't be able to fit a Nauti and two Radians in my '05 Civic, but the '05 is a particularly bad model year for three-across. Hers might be a little better. The only way I'd be able to make it work would be three Radians either installed RF-FF-RF (with angle adjusters for the RF ones) or FF-RF-FF (without angle adjusters).
I would suggest R120s for maximum flexibility.
Basically I think she needs to buy two Radians, see if she can make it work, and if she can't she needs a 3rd Radian.
If she absolutely can't come up with $600 for new car seats , then she probably has no choice but to move her 3 year old to the front seat. I would probably try to work toward eventually having at least one Frontier; If she's not going to rear-face the babies anyway, she could get Maestros for the twins for now and save for a Frontier later. Or if possible she could buy a Frontier for the oldest child, pass the Nauti down to the larger of the twins, and get a Maestro for the smaller twin. Eventually she can get a booster for the oldest, pass the Frontier down to the larger twin and the Nauti down to the smaller twin. She's got two kids who are pretty big for their age so I'm not quite sure how she's going to safely transport those kids without at least one Frontier eventually.