"She says that even though she has not sent the contracts back she has informed the vendors in writing that she has signed contracts and is holding them pending resolution of some minor queries."
But why sign contracts if you have concerns? I would say that you are in grey area, that the fact that contracts have not been exchanged is indicative of concerns but if your solicitor has made a commitment on your behalf then you are somewhat stuck.
By all means, walk away, but do try not to blame your solicitor for your change of mind and the possible consequences.
mf