Well, wearing a Ring will harden your erection - and prolong the erectile performance by slightly reducing the feeling in your privates.
At least that is what it did for me an some occasions.
Physiologically it does that by reducing the efferent bloodflow through the superficial veins, without cutting off the instream through the deep artries.
But like the feeling, when you cut off the bloodstream in one of your fingers with a rubber band, I found it quite uncofortable after, say fifteen minutes, max.
So whyever she proposed it....
-maybe she just likes gadgets in bed,
-or she felt your erection should be harder(do you remenber if you have been fully engorged?),
-or both your genitalia are not so well matched in size and she hopes to compensate for that by using a ring,
-or it all went far to fast for her and she has made the experience that men last longer with a ring....
I dont know and it does not have to say, that she did not enjoy your dalliance. But in my personal opinion - I dont like the rings.
If you are too fast, learn self-control. Slowing condoms or ointments are avaliable on the market.
If your too slow or kinda flabby, dont drink on those occasions, it reduces erectile functions. Or ask yourself why that is so.
Stress can be a cause, or you simply are not that into her. Or you are adipose or there is a medical problem....
And finally -If you dont see a problem - ask her if she does.
Maybe she really just likes playthings.