What are your plans for the fry? A 1 gallon won't last very long if she has a big birth load as they grow rather quickly. They definitely need a heater, and no filter is ok, if you can do daily water changes. Most heaters will get a tank that small too hot, so let it run for a few days and test the temperature to see.
I would personally just leave the most pregnant fish by itself on one side of the divider if you don't want to take it out, then watch her closely once she's squared off. When she had the babies, net them out as quick as you can before she eats them. Some kind of floating plant cover in that portion of the tank would be a good idea so they can hide if they are born when you aren't around.
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