Isadora - my favourite of your choices - Dorrie, Dorey, Dot are all also nns
Elizabeth - a classic -Lizbie is a very underused nn
Eloisa - it’s nice but I’d use this spelling which is the usual one - otherwise people will misspell it all the time. Essie is another nn
Adora - no, you just think of Adore and Adorable, which is wet and weird - I like Isadora best but Theodora and Dorothea both mean gift as alternatives
Crystalina - absolutely not - sounds like a stripper or fortune teller or possibly a brand of window cleaner -
Others -
Cecilia - Cece, Cely, Cicely, Cecily
Felicity - Issy, Lissa, Flick, Fee
Henrietta - Harriet, Hattie, Hetty, Etta, Henny, Hallie
Georgina / Georgiana - Georgia, Georgie, Gigi, Gina
Josephine - Josie, Jo Jo, Jo, Fifi, Ephie
Joanna - Josie, Jojo, Jo, Annie, Nancy, Nan
Rosanna - Rose, Rosa, Rosy, Posy, Anna, Annie, Nancy
Penelope - Pen, Penny, Nell, Pippa
Katharine - Kate, Katy, Kit, Kitty, Kathy, Kat, Kay
Francesca - Fran, Francie, Frankie, Franca, Chessie, Chesca
Alexandra - Alex, Alix, Alecky, Sandy, Xandra, Sacha, Ala, Allie
Susannah - Susie, Sukey, Sue, Susan, Zanna, Anna, Annie, Nancy
Maria - May, Maya, Mia, Molly, Polly, Maisie, Ria
Marguerite- Margot, Maggie, Peggie, Daisy, Rita, Margie
Victoria - Vicky, Vita, Tory, Plum
Natalia - Natasha, Tally, Tasha, Nattie