The modesty of painted bellies

Maybe if I wore long skirts and wigs, this wouldn't be a problem. Maybe then my views on modesty would be a bit more obvious.

I am a Jew. I am a traditional Jew. I do not follow Orthodox customs of dress (long skirts and sleeves) nor do I, a married woman, cover my hair. I do, however, believe in Tzniut--modesty. My daughters do not wear bikinis. They will not wear anything that leaves their belly button beared. Generally, the most skin I show are the elbows down to hands. Some O's would have a problem with that, but I don't. It's how I feel comfortable, yet honor the concept of Tzniut.

If I wear a top that's too low cut, I hold it up with safety pins. Yes, I do carry a selection of pins in my bag just for that cause. Now that I'm at that hugely pregnant stage, I often lift my shirt up at home so that I can watch a foot poke out here to the left or see a bum roll when he/she launches off from my ribs. There, with only my immediate family, you will see my stomach in its stretch-mark glory. Well, YOU won't see it because of the rules of Tznuit. My husband and children will, but no one outside our immediate home. When my brother came to visit, I never once bared my belly. When my parents were here, I had no urge to show them. When it comes to friends, I am the same way. My belly is reserved for me, my husband and my immediately family. I am not comfortable with having it on display in any way shape or form nor do I think it's appropriate.

I have a (goy) friend who had henna tatoo done on her stomach during her last pregnancy. It was lovely--just gorgeous and it fit her personality wonderfully. It was not, however, me. It's my understanding that she plans on having that artist do my pregnant belly. I desperately want to avoid that. I very much do not want that to happen. If I say that, though, I risk hurting her feelings (I hear she's been planning this thing for a while). If I go along with it, I will be annoyed with myself. How can I ask Hashem for protection in labor when I just so blatantly ignored not only His laws of Tznuit, but also my own conscience which He gave me?

I'm at a loss and I only have a few hours to figure it out.

EDIT: I called my friend and explained my feelings to her. She suggested we do the art on my hands which is what we did. I was MUCH more comfortable with that and she was thrilled that she got to do it for me.