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A small insect every 2 to 3 days should be OK.
Good luck!

Crematogaster sp. I think.

I'm not sure if she is Solenopsis. Might be Pheidole, Monomorium and others.
Can you make a few more photos?

Another alternative of the test tube can be a tic tac box.
I don't think you will need the nest already.

Be sure to provide her with water.

Solenopsis geminata I guess.

California is pretty diverse but to find more and bigger species you should head to the desert in summer especially after rain or in the mountains. Species you can commonly find there: Pogonomyrmex sp, Veromessor pergandei , Pheidole sp, Myrmecocystus sp. and more. In the mountains you can find: Cam...

Yes, Argentine ants.
One of the most common urban species in Southern California.

Linepithema humile.
You should add a few workers because she probably won't survive without them.

She is probably not dead! Often Northern Camponotus do that In very cold temperatures.
Once you warm her up she will start moving again.