Paracelsus! Nice summary on the problems of an oversupply of O₂.
Well, yeah, but that's not specific to O₂.
Another fun fact: Earth's atmo is 21% O₂. At 26%, wet vegetable matter burns... and now you have another reason to exercise: you're doing your part to save all terrestrial life from going fwoosh.
I mean, the Carboniferous was a thing in Earth's distant past, with atmospheric oxygen up to (at one point) 35%; it's what allowed freakishly huge insects, because one of the limits on their size is how much O2 their lungless, passive air holes can cycle. Regardless of the high O2, modern people still wouldn't want to breathe that air for too long because most parts of the sky would be hazy-brown from the soot of forest fires.
Re: atmospheric pressure, the opposite is true. At 18,000m/60,000ft. altitude, the overall atmospheric pressure is so low the water in your lungs boils away and you can't breathe regardless of how much oxygen is pumped into your lungs. It's known as the "Armstrong Limit" and is the effective limit for airplanes unless the pilots/occupants wear pressure suits or space suits.
tl;dr: Please do not take your thicc, cute wife back in time to the Carboniferous or to above the Armstrong Limit. She would not have a good time and/or survive. :<