How do I attach a screenshot to a rely email, not a new email

Hit reply, then click inside body and hold until you see options of inserting photo, video etc. and select the right option.

Your screenshot would/ should be in your camera roll.

How do I attach a pic to a reply email?

You just never know, with a billion add ons and permutations and cat and dog hair on the iPad or laptop interfering 😉

Glad it worked for you, Elbury!