The beginning of a long and painful journey

[Rawpain]

Okay I could do with a quick bit of advice. She is asking me to get the kids from my mums house after I finish work. She told my mum yesterday that I was picking them up but she had not asked me. She does not want to see my mum and last week turned up with a friend and didn not talk to my mum. Now she has just messaged to say she has an emergency at work and I need to have the kids tonight. I think she is lying and just wants to go and watch football with OM.
What should I do? Help