We are having a ‘surprise’ in [name]May[/name]. We have a 6 yr old boy [name]Jason[/name], who we’ve always called JJ, and a 4 year old [name]Ruby[/name]. I like the name [name]Susanna[/name] for another girl, but worry that if she is nick-named [name]Susie[/name], it sounds silly with [name]Ruby[/name]…‘[name]Ruby[/name] and [name]Susie[/name].’ I would prefer to always call her [name]Susanna[/name], but you never know how nick names will work out. I don’t dislike [name]Susie[/name], just wondering what others might think.
I think [name]Susie[/name] is somewhat inevitable. Other nn options for [name]Susanna[/name] could be [name]Sukie[/name] or [name]Anna[/name], but I think they’re less likely to come about. I don’t think [name]Ruby[/name] and [name]Susie[/name] sound silly at all - they work really well together, [name]IMO[/name]. 
I think [name]Susannah[/name] and [name]Ruby[/name] are a really nice pair.
Also, I know a [name]Susannah[/name] that goes “[name]Zan[/name]” as a nickname. So [name]Susie[/name] isn’t inevitable, especially if you don’t call her [name]Susie[/name] a home.
My adult daughter’s name is [name]Susannah[/name]. She has never been called [name]Sue[/name] or [name]Susie[/name] by anyone. Her family nn is Suzzie-pronounced with a short u.
[name]Love[/name] [name]Susanna[/name], if you make a point right from the beginning of clarifying for everyone that you want her to go by her full name she’s less likely to be called [name]Susie[/name]. A friend took that tacit when her daughter was born and everyone has always called her [name]Veronica[/name] and nothing else.
Disagree that [name]Susie[/name] is inevitable, and I usually think all nicknames are inevitable. I know a lot of Susannahs/Susannas (at least 4) and also some Susans who are always called by their full names. I think [name]Susanna[/name] and [name]Ruby[/name] sounds pretty together.
[name]Susanna[/name] and [name]Ruby[/name] are great, and those who call her by [name]Suzie[/name] wont usually be saying the two names together. I say use it! Congrats!
Nicknames can sometimes be avoided if you never use them yourself, and the child doesn’t like them either. I have a brother [name]James[/name] who has always been [name]James[/name] in spite of all the people who tried calling him [name]Jimmy[/name]. My parents were polite but firm that they had named him [name]James[/name], and later he himself was very assertive in correcting people!
If you want to offer a nickname (sometimes this pacifies the nickname-insistent) how about [name]Zuzu[/name]?
At any rate, [name]Ruby[/name] and [name]Susanna[/name] are a darling sister set, I hope you use it!