Hmm... That's a good question. I always assumed it was Louisa w/an S sound. It didn't occur to me it might be pronounced with a "z" until I read your post. I prefer the s-ending myself. But either way it's a lovely name.
I say it with the "s" sound and think it would be fine with Clara. I do agree that Louise is a nice alternative if you're worried about matchy-ness though.
With a z sound. I think Clara and Louisa are a darling sib set.
Married 10/4/2014 (10-4, good buddy!) Baby Boy #1 born 1/9/17 Baby Boy #2 EDD 11/4/18
"It's when you know you're licked before you begin, but you begin anyway and see it through no matter what. You rarely win, but sometimes you do." -Atticus Finch, To Kill A Mockingbird
Re: Louisa
Edit: I love this name either way.
Baby #2 Due 3/7/20
TTC #1: February 1, 2014
BFP #1: 2/21/14 EDD: 10/31/14 MMC: discovered 3/31/14 (blighted ovum) D&C: 4/3/14 at 9w6d
BFP #2:12/18/14 EDD: 8/27/14 Beta #1 (16 DPO): 50 Beta #2 (18 DPO): 54 CP: 12/25/14 at 5w0d
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Formally LisaG09
"Everybody wants to be happy. Nobody wants to feel pain but you can't have a rainbow without the rain."
Low progesterone
Baby boy born 01/2016
Currently: NTNP
me: 27 | husband: 35
IR PCOS dx Sept. 2014
married May 2015 --> started NTNP
BFP 6.28.15 - EDD 3.6.16
baby #1 born 2.19.16
TTC #2 in April 2017
BFP 12.30.17 - EDD 9.6.18
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Baby Boy #1 born 1/9/17
Baby Boy #2 EDD 11/4/18
TTC since September 2012