with poor wherewithal during my schooling, mom suggested to teach indigent young ones in my area. I began tution for poor students free but the parents of those young ones soon offered help many ways not necessarily by cash but mor by kind. Those humble beginnings comes to mind. If one has passion for a particular profession she or he might succeed. Free tution attracted many and later days it gave rich dividends. Regards. God bless.
Regarding those options the only thing i am not sure is how many of those can you work from india ... most of the projects asked for usa based address or some other such info. your sister can definitely look for suitable ones and try those to make some money while she goes on to recover fully . all the best. also if schools are demanding , may be she can try teaching in coaching classes for competitive exams or teaching basic computer classes and coding in institutions offering PGDIT etc .. they are pretty easy and less physically taxing as you only teach selected days for certain limited hours . i did this more than a decade back so kind of outdated with the current scenario. though i did see few eng graduates making more money doing this than a regular job during my india visits.
OP- I feel that you did not get a good sense of the teaching profession here. I come from a family of teachers- starting from my grandfather, my parents, uncles, and aunts, sisters/cousins, etc. Like any job, teaching also requires hard work but you don't have to be an athlete. There is no running around the kids, teachers are not required to do so. A teacher can ask for a chair if there are health issues and needs to sit and teach. She might need to take a flight of stairs but I am sure by the time she is back to the workforce she should be able to do it. Most schools have moved on to white-board and markers instead of chalk or she can buy her own anti-dust chalk. In my opinion, teaching younger kids is harder than a bit older. The middle-high school will be a good place for your sister to start. Once she has her lesson plans made, she can improve on those and don't have to start from scratch every year. Again, in my humble opinion, most kids are not spoiled brats, they are just opinionated kids.
Oh..I formed my impressions based on my school days I remember school teachers making rounds of all classrooms, coughing often due to the chalk dust, those days we dint have white boards, overhead projectors, markers etc...was not common for teachers to sit and teach unless very unwell. School where I studied was a reputed one, which has about 5 floors...no elevators...any teacher teaching higher grades would have to mandatorily climb stairs several times a day.. becos library and other facilities were in ground floor, assembly held in playground area everyday morning, and principal room was in ground floor..auditorium in basement... I remember teachers taking ruler and giving one on the knuckles for disobedient students...and screaming on the top of their voices " silence please!!!" ... I'm mistaken about all kids being spoilt brats but some kids definitely are...some kids dont want to make adjustments to accommodate another person while travelling in car ..even for short distances.. not bothered to even say hi or hello when a relative or other elderly person comes home...getting kids to open up and speak maybe tough...also saw a couple of school kids trying to throw stones on a stray cat...all are kids studying in top schools and good families...generally I felt it requires lot of training to deal with different mindset of kids. Very responsible job.