I like the name
Ruby. It's pretty, and I can't think of anything to dislike about it, really.
It is the name of a somewhat morally ambiguous demon character from the show 'Supernatural'. I don't think I've met or really seen/heard of anyone else with the name.
If I were you, I'd probably ask the SIL if it was okay with her that I use the name. If she's for sure not having more kids, I can't imagine her minding, but if she's still considering maybe possibly having another baby in the future, she might still feel attached to the name. Can't hurt to ask, right? Better than hurt feelings or whatever.
Of your combos, I like:
Ruby WinifredRuby Winifred ClaireRuby Claire Josephine
Other suggestions:
Ruby CatherineRuby MarcellaRuby Ava IreneRuby HopeRuby Ariana JaneRuby AnneRuby Cordelia Grace