Stain on Nia's outfit

So, I changed Nia's clothes the other day and found a stain on her shirt :/

I did try to get it off with some water and it got a bit lighter but it still bugs me. I was holding off on using any kind of chemical since I'm scared of damaging it, I don't usually wash my girls' clothes.

So I was wondering what you guys would suggest me using?

 

Here's a picture:

Put it in a washing bag, and stick it in the washing machine? I've done that with several Volks pieces and it's been fine.