That is a good question. Unfortunately, as far as I can tell, as long as your mother is in the skilled nursing facility, she cannot trigger the 60-day break in in-patient status necessary to start a new spell of illness even though Medicare is not paying for her care.
The Centers for Medicare and Medicaid Services provides that “a benefit period cannot end while a beneficiary is an inpatient (see §10.4.4) of an institution that meets the basic definition of a “SNF” at §1819(a)(1) of the Act, as discussed further in §10.4.3.2 below.” Check out the entire document online.
For more on Medicare’s limited nursing home coverage, read this article.