I'm not sure that 'we all know' you have to incorporate circuits. I know I don't do this. That's quite the assumption.
As far as adding a load for her to lift, particularly for legs, have you considered buying a sandbag? You could fill this up to whatever she can handle for sandbag carries and squats, and over time add more sand as she adapts to the load. This would be a good start. Pushups and pullups are great bodyweight exercises if she's capable of performing these movements. I also like lunges. Even at my size, lunges with no additional weight can be very taxing.
Also, rubberbands, like the ones elitefts sells, can be very useful, and inexpensive. I often do curls and triceps extensions with these, by standing on one end of the band or hooking it on something above me. They can also be used for pull up assistance.