Wait, if you want to check if the size is larger than label, how can .get_visible_line_count() help you?
I had the almost same problem before, i solved that checking using len(label.text)*font_width, and adapting the resulting number to what i wanted
If you want to adust it's height, i think your solution is better than the one i implemented:
I used split on ('\n') to check how many line breaks were there, so i could adjust the label with it