It seems to just take time to get used to. I’d say she’s right, it’s too small, for now. Try a bigger one (there’s like four or five aren’t there and you can adjust the gap). And then reduce the size over time.
But I think the main thing is you’re trying too much too fast. We worked up with him trying it for an hour, then a few, then a day, then overnight, etc. If you’ve just gone four days with nothing before no wonder you’re sore! Try some time out, let your body recover, get used to it, then back in again.
Also you need to be lubing the ring with a good silicon lube (others recommend coconut oil I’ve seen). Makes a big difference!
Hope that helps!!!