What would you do? Baby name trouble ahead.

What would you do? 
We decided on the name Ophelia Shae for our first. Previously, we were milling around "Sienna Jade" and made the HUGE mistake of telling my immediate family. Mostly, we got "that's a stripper name" as responses. It completely ruined things for us, so we decided not to tell anyone any other names until she's born and it's on paper.
I knew my sister-in-law, who has been trying for a second child for many years, has wanted a girl and wanted to name her Athena (not a life-long dream, but many years in the making). She has told me that she wanted another name, but a friend "took it" and she was furious.
I mentioned a list of names in passing to my sister, and she said "Hell no, you can't pick Ophelia--(sister in law) wants the middle name Ophelia for a potential daughter." 
We already picked Ophelia. We love it. Now I just don't know what to do. If I tell my sister in law to give her a heads up, there's a possibility that she'll be furious and then I don't know what I'd do. Family already crapped on our previous choice and I know it'll cause even more problems with this one. She isn't pregnant and won't be trying anymore after about a year. 
I must note that family is often completely awful to me (cruel), and I often bend to their wills because I don't want any controversy or backlash. This is our first and I shouldn't probably care what they think, but I find myself worrying anyway about the potential anger that comes from it--even though we've been calling our Nugget "Ophelia" for months now. 
What would you do? Would you tell her? I would love to just be honest afterwards, but I know my sister will enjoy turning this into a bigger mess than necessary. 
UPDATE: Would you tell the sister-in-law ahead of time to break the ice? 
Thanks for your responses! You're helping to give me some confidence. I loved Sienna Jade, too, but my husband said it got too tainted by those reactions--it's pretty true. The reactions were intense.