I do not know what power you have given her in terms of handling your account, but if you want to end any power she may have in handling it (or abusing it) you should reveoke any authorization to transact business for you and immediately tell the broker/custodian that you have done so.
Also, any spiteful action on her part causing you damage would be illegal and could caus eher to lose her license and subject her to damages under the securities laws.
BUT hey, she is your mother, you'll never have another one, and these fallings out usually do not last very long, so you may not want to further aggravate a tense situation.