@timespast Welcome to Mayo Connect. Let's talk about what might be happening here.
Your description of "...tired, heavy..." legs sounds to me like there is something besides joint replacement going on her.
Are you taking heart, blood pressure or cholesterol medications? These as well as some other prescriptions can cause this sensation as well as fatigue. Also, if you have asthma, COPD or another lung problem, heavy legs and fatigue can be symptoms of low oxygen. Your symptoms may also indicate low hemoglobin.
Maybe a visit to your primary caregiver for a full assessment is in order.
Have you had a complete physical, with bloodwork, since the symptoms started?