Adjusting Riding Mower for Short People?

My daughter has the same problem but she has learned to always check to see if she can reach the petals before buying. We had a regular size mower and the safety cut off button was under the seat so if she raised even a little bit to try to reach the pedal the mower would cut off. My son fixed it by fastening a block to the petal but you may even be able to strap a block on.

You may have this same type but the only way we could remedy it was to fasten a block of wood to the pedal as I've never seen any product sold for this purpose.
I would suggest you contact the store were you purchased your mower and tell them your problem as I feel sure they have heard of this problem.
I feel sure they will help you but, if, by chance, they tell you they cannot help you then you'll have to find someone that can do this.
If there is not a 'handy man' around that you can call on for help then you may have an expensive fix because the 'fixer' will have to have the mower at his place in order to attach something to the pedal and most likely you have no way to transport the mower anywhere.
You will have to have someone help you measure what size block you'll need but the wood will probably be 2x2's or 4x4's to match your reach. My son fixed ours but he has tools to work with and he cut her block on an angle but that may not be necessary.

I'm hoping the store will help you and send someone out to do the fix.
Good luck and stay safe.