Ideas for coming out to Siblings

My daughter (MTF) said that she does not know how to come out to her siblings. She is almost 15 and they are 12 & 13. They are all pretty close and they do have friends in the 2SLGBTQ+ community, so there is no safety concerns or anything, she just feels weird about it because they only know her as their older brother. Does anybody have any suggestions I can pass along? Her idea was to get some new clothes and just start wearing those, but I think it would be nice to have something with a little more clarification. Or would that work?? Any ideas are totally welcome. Thank you for your help.