I wrote a column on
Leanne back in 2011. I was quite surprised in looking at census records to discover this is a name which is much older than I thought. It was already being regularly used in the USA well before the Civil War. I think it is probable that
Leanna and
Leanne in English were originally short forms of Julianna/Julianne and so respellings of
Liana and
Liane rather than created by merging
Lee and
Ann.
Leanna was fairly common before
Lee was used as a girl's name.