Pretty sure. Its probably there just cause its an early lesson and they dont want to completely throw off people.. Idk
Indians would usually write ladki (the ड़ is mostly represented by d), but many even write larki (or larkee for that matter, we use the Latin script just to get the point across and because it's easier than using a Hindi keyboard which we are not accustomed to owing to the fact that they came out only recently).
र - It's a soft tone of "r" Just download google translator and translate words like Night - raat in hindi (soft r)(रात)
Secret -raaj in hindi (soft r ) ( राज)
You will understand .
But when you are using "ड़" , first of all keep in mind no word starts with this alphabet and it sounds like actual prounciation of english "R" . Like when you say "Rat"," Rattle snake" ,"roar" ...how you pronounce the "r" , It's a high vocal tone. So this is how you pronounce "ड़"
You can search on search on google translator words like - To fight - लडना ( lārna) To quarrel - jhagarna (झगडना).
I hope , i have made you understand.