Rough limits on Chris's magic:
Using Shove doesn't take too much energy. It's about the same as if she had actually shoved someone. It's really more of a cantrip than a spell.
For Barrier and Ward, it depends on how they're cast. Both spells were created with use of an anchor in mind. If they're cast on something metal, they conform to that shape and draw a small amount of energy as long as they're cast. (In the case of Chris's tunic, she cast it on the silver threads in the weave. The spell tired her as much as walking around in full iron armor.)
The way Chris is casting now, she's technically using herself as the anchor, but not being made of metal the spell would just collapse if she let it settle. Instead, she's forcing it to remain in the first stage of the spell, which takes almost three times as much energy.