I appreciate drawbacks of having to commit to a 1000 minimum carbon mold. That said from a (very personal) user perspective, at 60kg, even a well built 1.2kg carbon frame would be strong enough for her to jump it all day (I know, not for the big boys). So an alu or Ti frame (how nice I personally find it) built to last is already 800gr heavier than she needs. A carbon frame (over built for her weight) is as close as it gets for her (the 456C was strong as a tank). On the parts level you can only sensibly save so much. Alternatively we could try a strongish XC frame with a 130mm fork and a 2 degree angleset, but reach, BB height and seat angle numbers won’t be that great then (although sag and the angleset compensate a bit).
For now it’s between a Transition Vanquish or a Scandal with the money saved spent on lighter parts. With a carbon Scandal, the choice would be easy… 😛