Both are lovely! I prefer
Mabel as it’s one of my favourite names.
Elsie is nice, but I like it more as a nickname for
Elspeth, and it’s really popular right now. My favourite combo is
Mabel Rose.
Other suggestions: (basically my whole girls list haha)
AdaBeatriceBeatrixBridget CatherineCharlotteClaraClementine CoraDaphneEdithElizaEsmeHarrietIda JulietLillianLucyMargotMarnieMatildaMavisNellPrimroseRose SybilSylvieTheodoraWinnifred