Regardless of what the course may teach, it actually varies; the most common method is to reach up from underneath the shower chair in a non-weight-bearing resident/patient. However, depending on the kind of sling used, it may be done in the sling to ensure a more thorough clean, since you can see what you're doing.
Since you mention a standing hoist, I'm inclined to think they'd get her into a standing position and then clean her whilst standing. However, it would be a good idea to clarify this with the person training you, since each organisation has its own methods and policies.
For what it's worth, this falls into the category of "sensible questions". It's far better to ask if you're unsure, rather than trying to guess and getting it wrong.