I used to use one of these Ezy Dog Harnesses for Otto when I had to keep him on the Long Line.
It has a nice big neoprene chest plate to disperse pressure, although it was a bit wide for Otto and when he ran it rubbed his legs a bit.
Have you tried using a slip lead? I use one similar to these, Rope Lead, now he can go off the lead.
If you are worried about hurting her you could get something wider to ease the pressure. I have a really wide Aerborn one that I sometimes use. It is cushion webbing and very soft, in fact I don't use it much as Otto takes the mickey!