How to help my OCD sisterYour question is not complete in its information for a proper response.
What are the triggers for her thoughts? Please have her list down all the triggers one by one.
Get her to grade these triggers in order of severity.
Ask her to pick up the ones which are the least severe and face them without indulging in any compulsions. She will get very stressed but that is what will help her come out of it. If she continues to do her compulsions after she feels stressed, she will not be able to beat them.
She will have to keep practicing constantly. Remind her that when she was learning to ride a bicycle, she must've fallen many times. If she had given up then for fear that she would fall again and hurt herself, she would not have been able to learn cycling. If she has managed to learn cycling it is only because she persisted in her effort to beat the inability.
It is the same with OCD. The process oultlined is a procedure called Exposure and Response Prevention. Look it up on the internet.
Ask her to read Brain Lock by Dr. Geoffrey Schwartz. This book teaches you how to beat OCD at home.
Support her. Get your family to support her too. Remember she is two different people and the original one has no control over the other OCD affected one. Yelling at her because her OCD-affected side is indulging in compulsions is doing her an injustice. Know it and be with her in times of stress.
I wish you and her the very best.
I'm not a doctor. I'm a husband with an OCD affected wife. Reach out to me in case you need more help.