Can you rephrase it to : I'm a great mum and I do the best I can. Now i'd like you to say it to yourself first thing in the morning (before you get up), while you brush your teeth, at lunch, everytime you feel down and last thing before you fall asleep.
Now I know you are going to tell me that it will sound ridiculous (and it will because as I said your negative brain will try to fight it). For me it took me one week before I started to believe what I was saying: I deserve to be happy and I deserve to be love, and you know what I'm a month into saying it and I believe e it! My self love has been very high.
It's like the advice we get here :fake it until you believe it. Trust me on this one JujuB if you stick with it for at least 21 days it will be a massive 180 for you. There will be days when it will be hard but stick to it and you mind will shift from negativity to positivity.
I know you can do it. I will be by your side. Can you make that commitment to yourself for the next 21 days?