And if she is a "normal" height & weight woman you might need to get her a different trimmer, a full H harness and move the clip on the trimmer.
I use a strait shaft trimmer, my wife finds it too heavy and too long so she has her own bent shaft trimmer with an extra short shaft,
With that she can trim all day just as fast as me but with the Sthil she is knackered after about 10 minutes.
I wear the standard sling harness but she has those brest type things which made the sling uncomfortable however the H harness works really well.
I think it was actually an arbourist harness but she loves it so much she has repaired it at least a dozen times.