Does a stay for 3 weeks in respite care in an assisted living facility qualify for tax deduction?

[bwa]

It does if you were there for medical care. 

From IRS Publication 502:  "You can include in medical expenses the cost of medical care in a nursing home, home for the aged, or similar institution, for yourself, your spouse, or your dependents. This includes the cost of meals and lodging in the home if a principal reason for being there is to get medical care.

Do not include the cost of meals and lodging if the reason for being in the home is personal. You can, however, include in medical expenses the part of the cost that is for medical or nursing care."

As a general rule, most nursing home costs are deductible while only a portion of costs at an assisted living facility would be. The facility can usually provide you with a statement as to what portion are deductible.