Ungrateful daughter

You don't say how old the children are but if they are still small, she may be very frazzled. She sounds downright mean though and it is something I have noticed in my own family.
I rarely give money or loans to DC but if I ever have, I have never had a thank-you. It's as if they are embarrassed about the gift . People much prefer to be the benefactor than the recipient. I never expect gratitude. Come on now, you brought her into this world, do you really expect her to be grateful.!

Have a proper talk to her if you get a moment, and tell her your thoughts. Otherwise they will fester away inside you and get even more bitter.

I disagree about involving others. This is between you and her.

Please don't allow this to go on the blackmail is unacceptable stop the funding straight away and make her stand on her own two feet,you need to be strong about this do you have any other children who can put her right as to the way she is behaving if you do please get them involved.
At 34 she should be managing her own life and funds not relying on the bank of mum & dad.

Why do you run her car and pay for her phone?
If she is working and not earning enough she should claim working tax credits.

Emotional blackmail has to be the worst trait in anyone. I'd start tailing off the funding and see what happens. Who's going to help you when you're down to your last ? That's more of a worry than anything I think.