Have you noticed if she's using the litterbox normally? If not, she could have a urinary or intestinal problem or blockage, which is causing her to walk more slowly or gingerly.
However, since it's already been 4 days since she's exhibiting this behavior, I'd definitely have her evaluated by the vet, today. From your description of how she's acting, there's possibility that she WAS injured while playing with your male cat and if he's somewhat of a 'bully', he may have cornered her or caused her to jump down from a height (or she could have fallen) and this caused injury.
If it's not her nature to hide, there's definitely something wrong; cats will hide when they don't feel well and/or are in pain. Having her checked over by the vet and getting a definite diagnosis and then appropriate treatment, would be your best course of action at this time.
I hope it's something minor, and she's feeling much better, soon! Please let me know the vet's findings. Thanks!
Cher
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