One way kindness

I can understand why you are upset, but do you have evidence that she lied? Is there a history of lying or there is more to the relationship with your daughter, which you are not revealing?

How do you know she lied? She has children and needs to make sure they are safe. Do you have anyone else you could take to this meeting? Often people are forced to have to operate on their own in quite big decision making through no fault of their own or of those around them. Make sure you are well informed from all angles.

You've made up a scenario that may not of of even happened
If her friend cancelled last minute and she had no one to watch the children, what she was supposed to do?

Why don’t you believe her it seems a strong statement from you !
I can understand your difficulty because you really do need someone with you when you go to these important funding issue meetings but why are you thinking she did it to you on purpose ?
Do you normally have a good relationship with your girl

If she can’t get childcare, what are her alternatives? Also, why don’t you believe her? It seems odd that she would lie.

Parenting is sometimes is a one way street. But maybe give her the benefit of the doubt. I hope things turned out well for you and your husband.