She may have never been fully potty trained. If she is one of the yougest siblings it is likely she was put in underware before she was ready. I have seen this before.
Take her to a doctor. If nothing is wrong, try putting her in diapers. Tell her every hour to use the restroom. Try trianing pants first then if she still wets, put her in baby diapers. This is more emmbaressing than trianing pants (Pull ups or Easy ups). This gives her more initiative to stop peeing. Keep in mind not to have wear them around friends, This could be bad for her self-asteam. Tell her it is compleatly normal and knowbody has to know (don’t try to hide it from sibiling tell them so they know not to mske fun of her). If siblings poke fun at her consider putting them in diapers so they know what she is going through.
Hey thanks for the advise.