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The stress of moving the female could make her drop some of her fry, but it could also be a shock to her immune system. Now is a good time to just wait and observe. If she's really big, she could have dropsy. Look at her from the top, and make sure her scales do not stand out like a pine cone. If the larger tank has only guppies and plenty of floating plants, the fry should be safe and there will be no future need to move gravid females. Good luck, and keep us posted.