I wouldn't use
Belle as a mn because I don't like cutesyness and it's been done. [Google "
Liberty Belles."] I'd use a straightforward mn to ground the name and give the girl options for when she gets older and has her own opinions what she wants to be called. With a 3-syllable fn, I like a 1- or 2- syllable mn, so:
Liberty ClaireLiberty FaithLiberty GraceLiberty HopeLiberty JaneLiberty JuneLiberty LynnLiberty MaudeLiberty PaigeLiberty PearlLiberty Ruth
Although if you like cutesyness (no judgement - you do you), I'd try:
Liberty Bay
Liberty BrookeLiberty DawnLiberty DoveLiberty PeaceLiberty SkyLiberty StarLiberty Sunshine
Although if the baby's last name is one syllable, I'd think about:
Liberty HannahLiberty MayaLiberty ReneeLiberty Sarah
*****
And last of all an Admiral came,
A terrible man with a terrible name,—
A name which you all know by sight very well;
But which no one can speak, and no one can spell.
Robert Southey, "The March to Moscow"