To clarify, I am the guarantor because my MIL is collecting SSDI and while she has enough to pay rent, they wanted more insurance that she would be able to pay rent. She owned previously and has no past history of being a bad tenant.
Regarding the lease, it doesn't say much about the landlord's responsibility, but there are tenant-landlord laws that she is clearly violating. I found this online which seems to back me and my MIL in this case:
"Section 127L. When violations of the standards of fitness for human habitation as established in the state sanitary code, or of other applicable laws, ordinances, by-laws, rules or regulations, may endanger or materially impair the health, safety or well-being of a tenant of residential premises and are so certified by the board of health or local code enforcement agency, or in the cities of Boston, Worcester and Cambridge by the commissioner of housing inspection, or by a court of law, and if the owner or his agent has been notified in writing of the existence of the violations and has failed to begin all necessary repairs or to contract in writing with a third party for such repairs within five days after such notice, and to substantially complete all necessary repairs within fourteen days after such notice, unless a board of health, local code enforcement agency or court has ordered that said violations be corrected within a shorter period, in which case said period shall govern, the tenant or tenants may repair or have repaired the defects or conditions constituting the violations. The tenant or tenants may subsequently deduct from any rent which may subsequently become due, subject to the provisions of the following paragraph, an amount necessary to pay for such repairs. The tenant or tenants may, alternatively in such cases, treat the lease or rental agreement as abrogated, pay only the fair value of their use and occupation and vacate the premises within a reasonable time."
Is there anything in particular you think I should be looking for in the lease? I read the whole thing a couple times and I don't see anything that is relevant to this specific case so I am deferring to the laws in Massachusetts cited above.