pŏŏtka, or pŏŏptka, ... she would tell me it meant, 'doll' or 'baby doll' in Polish.
It's German dialect, not Polish. Puppke is a diminutive of Puppe, which means doll in English, so little doll is a good translation.
Your grandma apparently lived in an area under German or Austrian rule at the time, and/or spoke a dialect of Polish which was heavily influenced by German.