Busy girl! Do check her over for mites since she's been to parts unknown- they can transfer to the chicks who don't have as much to 'feed' them.
As for how long they stay together- as long as momma wants them. I've seen hens wean their chicks as early as 3 weeks and as late as 2+ months, it's all up to her and her hormones.
I too gauge it on weather- especially with that many babies (because she's not going to be able to cover everyone for very long). If they have shelter they can get in and out of, they tend to be smart enough to come in out of the rain, even something as simple as a board of plywood against a fence -- wired so it can't come flopping down in wind! I drill holes in the top and run a wire through, and then attach to something sturdy, makes a great run-to shelter that's cheap and effective.
The other consideration is how the rest of the flock takes to chicks. Mine is so used to broodies with babies they just roll their eyes and continue about their business - so watch and see how everyone does together. Generally by the end of the 1st week, the chicks have gotten over their 'pollyanna' stage where they are clueless to danger and by then their legs are a little longer too!
Beautiful family!