Should I ask her if she would like an "injection" as well?

Ask her if she would like you to look at hers... to reduce the awkwardness of course

Okay, so between now and tomorrow, I have to get REALLY flexible... or I can just ask my little sister to draw them for me, I'm sure she won't mind.

draw a rage guy on the left cheek and forever alone on the right one. and draw the trollface on your asshole and put "date?" on your gooch

Is there anything I should remember to do/say to them to make their job more comfortable?

Okay SA, every day for the next week I'm going to have a woman look at my bum and give me an injection.