Regarding getting specs on the well, one source would be to ask the well company who's name is on the well cap or on the pressure tank. The county may have records too. It varies.
If there is indeed a 5 or 6 inch casing, there would be room for chlorine pellets (about 3/8 or 5/16 inch diameter) to be dropped past the pump. That makes getting chlorine to the bottom of the well faster. I have a 4 inch casing, so I had to use only liquid; I allowed more time for water to circulate.
Hopefully the casing is out of the ground around a foot, with a well cap, rather than being in a pit. So if she sees something after lifting the well cap, it could be a hanger for the pitless. It could be something else. As long as there is room to drop pellets and/or pour bleach and water, this should not be that hard. If pellets are going to work, you would want to get pellets too. Bleach is easy to get of course. The vinegar in a big jug can be a little harder to find but smaller bottles are readily available. You can alternatively use muriatic acid, but that takes a lot more care. For sure you would want pH paper, and you would have to allow more time for the pH to stabilize to see if you want more. Vinegar is such that adding too much won't make things get way too acidic. It's kinda self limiting.
I have a powered anode in my water heater. I ordered that before I decided to get the iron_sulfur backwashing filter. If the other steps of chlorination and anode work do not handle the sulfur smell well enough, consider a backwashing iron+sulfur filter. That goes right after the pressure tank in the order of things. You still want to do the sanitizing in any case.