What a strange relationship you have - don't you trust her? If she is an unconrollable spender perhaps I could understand it.
A joint account is exactly what it says. Both parties have access to it. You may be able to set up an account with your bank where your wife has withdrawing rights, but only on a cheque which contains both signatures but you would have to talk to your bank manager to see whether this would be possible.
Otherwise, set up a separate account for her and arrange a monthly standing order into it from your own account and take out an insurance policy for her, written held in trust, so that she can receive death benefits without waiting for your Will to go to probate. But if she has no other money apart from what you give to her, how could she cope financially if you had a stroke or were taken into hospital and couldn't get to a bank to withdraw money for her?