Overweight nurse unable to physically manage her responsibilties

Advice please..

We have a very heavy nurse that works in our SNF. She is very pleasant to both residents & coworkers, she is very reliable and always comes to work, picks up extra shifts when needed, etc. Her actual nursing knowledge is average at best (does need some guidance with appropriate decision making skills related to resident clinical needs). She has been employed by the facility for several years now.

The problem.. she has always been very heavy and as she has aged (probably around mid to late 50's now) she is having increasing difficulty moving about the facility and being able to manage physically providing care. She requires a cane to walk on the the unit, leans heavily on the handrails for additional support. Takes an office chair with her on med rounds so that she can sit as she is gathering meds for each resident, leans on resident beds to support herself for treatments (think both elbows on the bed propping herself up and only using her fingers) and I can't imagine she could ever do CPR.

We admittedly have been turning a blind eye to her for some time because she is really a nice lady with a big heart. Not only do we not want to "hurt her", we also have to take the whole disability act into consideration. We also know she is probably the only working adult in her family and they rely heavily on her income.

The ugly.. We can't keep ignoring this. We have had 2 family complaints within the past week. Both families saying, "although we really like Nancy nurse, we are afraid if Mom had a medical emergency Nancy Nurse will be unable to physically care for Mom." Once said her physical disability is impairing her ability to provide safe care (it takes a very extended period of time just for her to get down the hallway).
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For all you experienced managers, how do we best handle this?