How to tell my parents this?

Its picture day next week on Thursday. I wanna straighten my hair, but that's my sister's straightner. My parents are pissed because I cut my hair. Its against my religion to cut my hair. I felt like I was left out at school ( I'm in 8th grade). This is spring pictures. In fall we had picture day and it was for our ID so that's what I told her and I don't know what to tell her now. My mom checks my hair every day to check if I cut it. I have to do a regular braid to school every day. I don't want to do this on picture day so what should I do? My sister is really mean. She's like in her own little world. She's a senior. I need help?