How can I ask my step mum for help with an eating disorder? (bulimia/anorexia)?

Im also bulimic and anorexic...my mom found out by seeing a note i wrote explaining my feelings i wasn't intending on her finding it but she did and now things are better. So you could always write a letter or note to her (kinda like I did only intentional) or if you just want to vent get on websites like sixbillionsecrets and state how you feel because its completely anonymous but remember the only person who can make you stop is you.Also,if none of that works you could always try to talk to somebody who is bulimic/anorexic like on a chat room or maybe a friend.Good luck!!