I would definitely go [name_f]Margaret[/name_f] [name_f]Eila[/name_f] if it were me. I think honouring a niece who has passed away should be top priority. It also doesn’t hurt that [name_f]Margaret[/name_f] [name_f]Eila[/name_f] is a beautiful, feminine name.
If you wanted to pick a girl’s name starting with B, I would suggest
[name_f]Brielle[/name_f]
[name_f]Brienna[/name_f]
[name_f]Becca[/name_f]
[name_u]Blair[/name_u]
[name_f]Belle[/name_f]
[name_f]Bella[/name_f] or
[name_f]Brianna[/name_f]