For some reason, I just can't like
Ruby. I can't give you a reason why but given how much others seem to like the name, it's probably just my personal hang up lol. Anyway, I have heard of one instance where I liked it,
Anna Ruby. It's the name of twin waterfalls in the state of
Georgia. Very pretty.
By the way, since you know your SIL wanted to use the name, talk to her about it. Tell her that you love the name and maybe even ask her blessing to use it since she has such a personal connection if you feel necessary.