I know it's easier said than done (my 3yo often attempts to stand or climb into the table
) but I'd insist that she sit or kneel, not stand on a big chair. You could perhaps say that you need to keep her safe so if she doesn't sit/kneel then you'll have to put her back in the high chair for her safety (and follow through with this of course if she does stand again). Hopefully she'd learn quite quickly.
Alternatively, like pp suggested is to get a tot seat (we used one too) or a booster seat that you can clip her in to. My DD was in a booster seat from about 2-2.5 yrs. not so much for the height but for keeping her safe and to address the issue you've raised.