Whether he took far too much or not, it's certainly far too early to be worrying about no signs of regrowth. Laburnum can sometimes be quite late showing signs of life, and I certainly wouldn't be worried at all until April.

Do you know when this 'Gardener' pruned the tree. If flowering trees and shrubs flower before June, the rule of thumb is prune them immediately after flowering. This allows the tree to develop new branches on which next year flowers are produced. I have laburnums in my garden and they are never pruned. I will be surprised if he has killed the tree but she may not get flowers this year. Bamboos advice is sound and all she can do is wait and see. If the tree made no new growth since the pruning she will not get flowers this year and may have to wait till next year for a show.

Agree re the flowering, unlikely to get any this year - if she wants to prune again, should be done immediately after flowering - or in this case, immediately after it should have flowered.