It is possible to introduce a new mouse with your current one but it has to be done slow and it is possible she won't want company anymore.
I suggest buying a pair of females and keep them in their own home. Introduce your current female to them on neutral territory (bathtub, a rubbermaid container etc) to see how they will get along. Let them spend more time together on neutral territory and after a couple weeks of this if they don't fight or only fight a little bit, wash the separate female's cage completely, and all contents. Put in fresh bedding etc, all the furnature back in and put the mice into it at the same time. Let them alone but watch from a distance or at least listen from a distance. There may be some squabbling as they establish a matriarchy
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PHLdyPayne