I would go slow here too Ziggy, but not knowing the details, which you have a perfect right to keep to yourself, none of us can give any more helpful advice.
Times have changed; our children's generation keep in contact at very rare intervals, even when there hasn't been any disagreement. Nor do they feel obliged to apologise just to smooth things over, as many of our generation did.
Basically, if they keep in touch it is because they want to, not out of a sense of family obligation.
Your daughter wants some contact, which is good. It sounds to me as if she is dealing with some things that are worrying her, these might have nothing to do with you, you know.