Theodora gets my vote, only because I adore the nn Teddy on a girl. I'm not a fan of Isadora or any of its nicknames, but here are some options that I can think of:
Theodora:
Theo
Thea
Teddy
Dory
Dora
Isadora:
Isa
Dory
Dora
Sadie (a bit of a stretch, but I actually like this one!)