I have very fine, thinning hair. It was dry from a perm in July and yesterday my hairdresser dyed it. I asked for a honey blonde (my hair is grey) and she dyed it a medium brown. I'm 71 years old and the color is MUCH too dark for me. How can I lighten this without doing more damage to my already sensitive scalp and hair?

There are artificial colour removers out there, but you may need to use it several times.
A less damaging way to help fade colour is by shampooing it with a detox/clarifying shampoo. The more you use it, the more the colour will fade. It is quite drying but then you can use a conditioner after you've shampoo'd. :)