How to sue for wrongful eviction?

She should be able to file in small claims court, or in housing court, if your town or city has one. (Some do.)

When she does file, she should be sure to sue for all costs incurred as a result of landlord's illegal action, including her cost to live somewhere else, expenses for anything she had to replace or pay because she did not have access to her own belongings, etc.

She should also call the state bar association. Many bar associations facilitate their members performing pro bono (charitable or free) legal work and could possibly make a referral to an attorney who would help take on her case. Also, depending on her age, she might try contacting AARP--they might have attorneys who would help the elderly who have been evicted, or be able to make a referral to some group that does.