The OP talked about how/when she did it earlier in the thread.
Bumbley, I know. She mentioned she uses two slow cookers.
The fact is, for a curry, she will still need to prep her ingredients, and sweat onions, spices and brown off meat before she puts it in the slow cooker. That's a pretty substantial job for 20 portions. Again, with something like jerk chicken, you are really looking at marinading; who has the fridge space to marinade enough chicken for 20 people?
When I cook for 20+, I hardly ever do a one-pot because the risk of screw-up is just too great (something goes wrong and the whole lot is wasted) and it gets tricky in a domestic kitchen with domestic oven/hob to cook that kind of volume in one go. I could only brown four thighs at a time on my hob, so it would require ten batches for me to brown 40 thighs -- that could very well take me nearly three hours and I would need to be continuously present at the hob.
I would also query the chap that does the English breakfast. I once, in my younger years, worked for a greasy spoon. Believe me, frying 20 eggs so 20 people can eat at roughly the same time is not easy. And you would have had to do your bacon, your sausage, your beans, whatever beforehand -- and toast ... toast for twenty people? The risk of it getting soggy if you are not in a commercial kitchen is high (you need a lot of racks and a commercial metal toaster). Some small greasy spoons can't even sit 20 people. 
I guess what I am trying to say is that cooking for 20 people kinda falls into the realm of a "catering job" more than anything else. There is a reason you always have to book if you are a party of this size in a restaurant and you want to eat together. The only time most people do this type of food is with Xmas dinner, and even then, most families do not cook for 20 -- and stress levels tend to go through the roof.
To me, the circumstances the OP describes are almost beyond the issue of sexism because cooking for 20 on a fairly regular basis is simply not something that has ever been particularly expected of one woman on her own within a traditional framework. It is specialised work, work that cooks and chefs do ... usually with help.
I am trying to think of traditional situations in my and DH's cultures (and DH is from the Middle East so it can be very different in terms of expectations) where ordinary women would be expected to do something like this, and all the scenarios (hatch, match, despatch, festival days etc), all the women of the family would get involved -- and to be fair, the men would help as well, particularly if it involved grilling meat. It would never be expected for one woman to do it on her own.