It can be quite involved, being an Occupational Therapist (OT). My easy child is one. It took her four years at uni studying this specifically. If her degree is already in some area of health sciences, she could get some advanced standing in a more specific Occupational Therapist (OT) course. Other possibilities are Diversional Therapy and Physiotherapy.
An Occupational Therapist (OT) deals with the interaction between a person with a disability (temporary or permanent) and their environment. As part of this, they will assess a person to define the level of impairment - what is affected and how much - and then look to see what they can put in place in that person's environment to help them function more effectively. For example, an Occupational Therapist (OT) will look at hand-rails, at special seats, at other ways a person could do various tasks. Over the weekend when easy child was visiting, I got her to assess my range of movement to determine which muscles are affected by my current flare-up of pain symptoms.
When it comes to various aids - at some point it becomes a physiotherapist's department. A physio will also look at range of movement but will be looking at how to get the person back to better functioning either by exercises, providing aids (such as crutches). A Diversional Therapist will look at how to keep a person happy and productive, either in terms of hobbies or maybe changing career options.
IN the case of a stroke patient, for example - they might have a Speech Therapist examining any speech or swallowing problems. An Occupational Therapist (OT) will examine their range of movement and strength in order to assess what they are likely to need help with. Having difficulty holding a spoon? An Occupational Therapist (OT) will find a different spoon or some way of attaching the spoon to the person's hand, so they will still try to use their weak hand to feed themselves. The physio will provide strengthening exercises and practice to help them build up the strength in that hand. The Occupational Therapist (OT) will put in any grab rail in the bathroom and make sure any mats are either non-slip or removed. The physio will visit and work the patient through various exercises and activities. The Occupational Therapist (OT) will provide a range of utelsils that may be easier for the person to use, and observe to see how they manage.
Meanwhile the Diversional Therapist will also be in on the act. The patient likes to knit or crochet? Then the Diversional Therapist may work with the Occupational Therapist (OT) to develop a new way to hold a crochet hook.
And so on. There is some degree of overlap and so you need to be able to compromise and adapt, also to work in harmony with other people and to delegate. You also need to work with other health professionals especially doctors, so you can get the information on the patient's health record and have a good understanding of the expectations of the health outcomes.
Maybe a good starting point would be to call a local hospital and ask to talk to the OTs, the physios, the Diversional Therapists etc. Ask them how THEY got their qualifications. Then maybe call the relevant teaching institution and talk to them. The way it works will vary from one country to the next. For example, at Sydney Uni there is a general health sciences degree course, you can jump from that to anything from a medical degree to radiography to physio to dentistry, to pharmacy - anything. husband's niece is currently studying something similar in WA, she wants to be a radiographer. By the time she finishes she is still free to change her mind - she could switch to nursing, or be a doctor if she chooses.
I hope your sister in law can work out what she wants and switch without too many problems.
Marg