First of all, never use synonyms just for the sake of using synonyms. Use the precise word that communicates your meaning — this will depend not just on your meaning, but on the context (which may change from one sentence to the next). It’s probable that none of those three synonyms would be useful to you. “Bachelorette” is only used in specific contexts (mainly "reality" TV). “Lass” is mainly used in Scotland. “Maiden” is old-fashioned. How old is the girl in question? Also, are you using “girl” mainly to indicate her age (in contrast to “woman”), or her gender (in contrast to “boy”)?

All of these are outdated. I would look for other synonyms. Young woman, is good

'Lass' is a rarely used word that is used in/around Scotland. It means 'young woman' or 'young girl.' 'Maiden' is a very old word that was used in the 1700s-1900s, and it usually means 'an unmarried woman.' It could also mean a beautiful girl! 'Bachelorette' means a woman who is getting married soon or is looking for a husband/wife. Bachelorette is commonly still used, but only in certain circumstances ^^ If you want a more used synonym for "girl" you could use "young woman" or "young lady" instead!