My bank doesn't allow the transfer of funds between accounts unless the account titles are identical.
Really good rule; eliminates a lot of problems.
As to the UTMA, it appears that the custodian is breaching her fiduciary duty. If a review of her account activity after she transfers funds from the minors account supports that conclusion; i.e. the money is not being used for the sole benefit of the child, terminate the account.
Note, if you had the first rule in place, you would not have this issue at all.