Have you thought about talking to your dad about keeping the money for you? Or maybe a grandparent? Maybe you can get a lock and key cash box to hide. In any previous hiding spots you had, leave a note for her about her theft
Another thing you can do is tell people not to give you money because your mother steals it from you. Embarrass her into leaving your money alone.
Your mom cannot take " your money " file a theft charge with the police.
How do you handle it? Obviously you have to ask her. If you have brothers or sisters, one of them might have taken it and not your mom.
You have to complain someone who can give you justice.
find another hiding place