Being the stubborn Taurean that I am, I would stick with Ruby! I also love Isabella but Ruby really is a beatiful name.
Apparently when I was born 31 yrs back my Nanna scoffed at the name given to me (Kate). As far as I know, it was perfectly acceptable and she sang me a beautiful song "KKK..Katy...Beautiful Katy...you're the only on that I adore.." etc up until she died last year.

Your Mum will get over it!

xxTaurean78