My ancestress Elizabeth Eichert married Adam Nicely (Kneissle) whose parents emigrated from Germany (then Bavaria) (earlier Kniessles said to have come from Switzerland) Adam's parents Anthony Kneissle and Elizabeth Yeager were born in 1710 and 1714, respecively. Anthony and his brother Adam emigrated to Pennsyvania along with a friend Yeager, probably Elizabetyh's brother, the Niceley-Yaeger marriage took place in Philadelphia so my guess that they met through her brother. Their three sons Anthony Adam and Jacob settled in Ligonier valley,but Jacob moved away after his family was killed in a series of indian attacks.
I'm not sure when Elizabeth Eichert was born, but a good guess, based on her in-laws birth dates would be the late 1740's through early 1750's. The eldest child I have a birth date on is in 1770 and the last in 1790)
Does she fit in with your Eicherts? I don't know where or when she was born, whether in the U.S. or Germany. I know Anthony Kneissle died in Westmoreland Co. Pa.