I think that if you went with [name_f]Magnolia[/name_f], even if your husband called her [name_f]Maggie[/name_f] the majority of the time, you could still use totally both [name_f]Magnolia[/name_f] and [name_f]Maggie[/name_f]. Though I understand your point that [name_f]Aggie[/name_f] is less common so it might be less likely to “take over” as the default name.
[name_f][/name_f][name_f][/name_f]I also think no matter what name/nickname combo you use, and how often you use each name, there’s always the chance that your daughter will eventually want to exclusively use the nickname (or only the full name). It’s hard to predict what will stick, so I think genuinely liking both options is most important. But if you’re not totally enamored with [name_f]Magnolia[/name_f], it’s probably worth considering additional options.
[name_f][/name_f]You’ve considered most of the obvious options already. I think they’re all nice names. [name_f]Margot[/name_f] is definitely somewhat trendy right now, but I wouldn’t let that stop you if you love it. It’s also possible that it’s less common where you live – you could check state-level statistics in the US or ask around if your friends with kids know a ton of little Margot’s. [name_f]Magdalena[/name_f] and [name_f]Margaret[/name_f] are great, classic-but-not-too-popular options. I think [name_f]Marigold[/name_f] may be a little too close to your niece’s name, though it could depend on how often you see your niece. And [name_f]Agatha[/name_f] is certainly still a little old/clunky, but I do like it personally! I think it’s ready for a revival – so many vintage names are coming back that I don’t think [name_f]Agatha[/name_f] will be too out of place. Same goes for [name_f]Agnes[/name_f]!
[name_f][/name_f]Some additional ways to get to [name_f]Maggie[/name_f] or [name_f]Aggie[/name_f] could be:
[name_f][/name_f][name_f]Augusta[/name_f] (this especially feels less likely to be nicknamed by default!)
[name_f][/name_f][name_f]Madrigal[/name_f]
[name_f][/name_f][name_f]Magda[/name_f]
[name_f][/name_f][name_f]Abigail[/name_f] (although people might default to Abby)
[name_f][/name_f][name_f]Marguerite[/name_f]
[name_f][/name_f][name_f]Margalo[/name_f] (similar to [name_f]Margot[/name_f] but less common!)
[name_f][/name_f][name_m]Agrippa[/name_m]
[name_f][/name_f][name_f]Dagmar[/name_f]
[name_f][/name_f][name_f]Dagny[/name_f] (maybe wouldn’t have a nickname, but it has a similar sound while still being a “full name”)
[name_f][/name_f][name_f]Madigan[/name_f] (might get [name_f]Maddie[/name_f] by default)
[name_f][/name_f][name_f]Magenta[/name_f]
[name_f][/name_f][name_f]Mahogany[/name_f]