A shady friend for torrid days
torrid vs. frigid
Temperature metaphor for emotional needs—easy to find friends when you're happy ('torrid'), harder when you're depressed ('frigid hour of mind').
vane a little to the east
Weather vane shifting east means wind change. Even slight shifts in opinion ('vane') scare away weak friends ('muslin souls').
fabric hierarchy
Muslin is cheap cotton, organdy is sheer and delicate, broadcloth is sturdy wool. She's ranking people by their emotional durability using textile prices.
The weaver
The weaver is God. She's asking if God is responsible for making some people weak and others strong—then immediately backs off with 'bewildering thread.'