You need to be honest with her. Does she know her DS is like this with your DD?
I don't work but rely on my friends quite often to look after my 2 kids & they also do the same with me. I would be gutted if they made up an excuse as to why they couldn't/wouldn't look after my kids. Despite her seeming like she isn't an organised person in regards to childcare for her children, I don't think you need to be hard on her. She probably just needs to be told is straight, she might not realise how it seems?!

