Has she been tested for Johne's disease? Any diarrhoea? Is her appetite good? Any problems with teeth? Is she arthritic?
If she is otherwise healthy - soaked beet shreds, Readigrass or Alpha A will help to put on weight, but not quickly. Lots of hedge browsings/branches when greener will also be appreciated.
But at over 10 years old she may also have come o then end of her life, especially if she had been in a commercial herd, where life is often a but harder on milking goats.