I think we need a few pictures of your plant for a proper analysis. It sounds like they either finished their pre-flower stretch or its just the pot size. How old are they?
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Multiple problems, mainly your roots. Probably not enough drainage and over-watering. Your roots are not able to breath and are under-developed. Now they can't use all the nutritions the plant needs.
Get some good substrate, maybe even invest in bio bizz. At least perlite for your substrate. And re-pot asap. Its not too late, she will be back if you give her the chance.