'Old Betty's joints'

Rhyme foretelling rain: 'Old Betty's joints are on the rack';

this is from a poem by Dr. Edward Jenner (1749-1823) who by the way discovered the smallpox vaccine; the poem is called 'Signs of rain' and the text goes like this

'Hard how the chairs and tables crack!
Old Betty's joints are on the rack;
Her corns with shooting pains torment her,
And to her bed untimely send her.

I'm not sure about the line
Old Betty's joints are on the rack
Is it an Irish or English rhyme foretelling rain and if so what's the origin and who was Old Betty?

Thanks to ESC for contribution on whistles.

An old person's joints sometimes ache when bad weather is coming. I can tell you that from experience.

Old Betty could have been anyone named Elizabeth who had arthritis.