Just echoing what others have said. If she is sectioned it is an indication of how very ill she is as they do not section unless they are absolutely sure it is necessary. My mum was under section 2, then extended to section 3 and we have just been told that she she is going to under section 3 for a further 6 months. It has been a tough lesson to step back and let the professionals deal with it, and I am only now accepting it with less guilt. Try to think of it in terms of a physical illness, if she had a broken leg and you didn't seek medical help it would be the opposite of caring, it would be cruelty.
If she is sectioned try to take time for yourself. She will have round the clock care. If she is moved onto a section 3 after a month, then she will be entitled to free care afterwards, either in a care home or in her own home. Do not underestimate what an enormous relief that can be.