TelHill: I'd like to join
HappyChappy in welcoming you! You won't be able to change your mom, but you can change the way you react and interact with her. There is a lot of good strategy here, that you could find helpful. Check out the links to the upper right of this post.
Have you thought about possible locking some items in a suitcase or getting some type of storage trunk (with padlock) to use at you mom's house to lock up the type of items your mom is apt to take? Even if you don't use something suitable to deter a seasoned thief, just presenting a situation where she would have to cut off a padlock (or break into a locked suitcase) might stop some of her actions. If you have your own vehicle at our mom's house, you might want to use the trunk for for some items that are of value to you, but not to someone who might break into the trunk of a car.
What other disturbing behavior does your mom exhibit? Some of the communication strategies could help you tame some of your mom's behavior from your prospective. The links below that relate to validation and stopping arguments might help you.
VALIDATION VALIDATION - DON'T INVALIDATEAVOID CIRCULAR ARGUMENTS