Obvisouly the older girls spin the ball better and lefties can produce some different looks, but to be honest I don’t see a big difference in productivity against lefty or righty pitchers.
My oldest DD (lefty slapper) hit them equally well until she played her first time in her town’s rec league. At this point she was still playing 12U in travel, but the Rec league was 14U distance with older TB pitchers. The extra 3 feet gave those lefty pitches a lot more break to her. She usually ended up hitting away until we got her mechanics back.