Unless WI law permits a person to break a lease due to medical condition, or the lease itself has a provision, most likely your mom is legally bound under the rental agreement.
Of course, she can move and see if the landlord pursues her for unpaid rent for damages. The landlord has a duty to mitigate damages by making a good faith effort to re-rent the unit so that the landlord's damages are minimized.
I hope this response was helpful.
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This is an unfortunate position to be in. I am not aware of any WI statute that allows for a lease to be broken under these circumstances. However, the landlord *may* be amenable to simply releasing your mother given these circumstances. Have you tried simply negotiating with him about it?
If your mother breaks the lease, the landlord has a duty to mitigate his damages by attempting to re-rent the premises.