I think
Elvira is a lovely-sounding name, especially the el-VEER-eh pronunciation.
Definitely a simple middle name.
Rose is okay, but I'm not sure about two 'r' sounds so close together... depends on taste I guess. I'd recommend
Lynn, Day, or
Poppy for similar names.
Also - depending on where you live, people might associate
Elvira with
Elvira, Mistress of the Dark (a character portrayed by
Cassandra Peterson) or the song
Elvira (by
Dallas Frazier, most famously covered by the Oak
Ridge Boys). I'd avoid using it for those reasons, but if someone I knew still used it, I wouldn't be weirded out.