Simcha tends to be more of a male name - but it is by no means unknown for girls. The girls' name
Aliza has a similar meaning. (Don't forget that loch ch sound in
Simcha, though!).
I like
Tamar - and that "date palm" meaning. There's a river in south-west England, near Plymouth, the
Tamar (pronounced Taymahr) so with that pronunciation it could easily work as a "water/river" name.
I prefer
Tamar to
Tamara but the latter could grow on me, despite the "tomorrow" jokes).