I can relate to your feelings of being a bad mum. I have 3 children and have struggled with my MH for a while now. I often feel like I let them down and they deserve better than me.
However my children are 26, 23 and 19 now and all three of them have been or are at University and are happy, well balanced adults with successful lives, so I couldn't have been a bad Mum. I have brought them up by myself for 15 years with no support from their Dad.
Look at your daughter and how well she is doing and give yourself credit for all that you do for her. Yes there are times when things are hard but that is life with MH. You are doing a wonderful job.
However it does make me angry when I'm struggling and people say 'what about your children' I want to scream 'what about me!' You are important so look after yourself
It's hard to keep a secret when it's written all over your body.
It makes you feel able to cope with life, while at the same time it's destroying you.