Being honest is one thing. She's just being nasty and passive-aggressive.
If she was going to tell you that you were not her best (yeah, not a good thing, to fish for that kind of response from anyone, but it is what it is and you can't take that back now), then at the absolute, barest minimum she should have either told you something good about your relationship (not necessarily about your sex life) and/or something you can improve in the bedroom department which is realistic.
Instead she turns you into Don Quixote, rather than Don Juan. You're not feeling like this is a great relationship and your care and love (including physical) can conquer all. Instead, she's got you tilting at windmills, trying to chase an impossible way to "get better".
If "refractory period" (I have never heard of such a term although I experienced it with a guy who was in his 20s -- that sort of stamina is for the very young) matters so damned much to her, then get some toys and give her added stimulus (or have her do so herself) while you recover between bouts.