Did you have sex already or not?

You had a missed opportunity when you mentioned a stress reliever. When she sent her "stress reliever" you should've said, "I had something else in mind".

Now you should definitely riff off of the cardio question she has. Completely ignore her second message.

I'm not sure how sexual you guys have been in person or through text so you'll have to calibrate my advice on what to say so it's not out of nowhere if you've never sexualized with her.

Her: "What kind of cardio"
You: "It involves two people and a lot of coconut oil"
or

You: "I'm not sure you could handle it smirk emoji"
Her: "I could" etc.
You: "Let's just say it involves handcuffs ;)"
or
You: "Let's just say it involves two people and a lot of coconut oil"