Congratulations!
Classic (short-ish, to match Grace) first: Amy, Anna, Daphne, Eve, Faith, Fern, Hope, Isabel, Joy, Juliet, Lea(h), Lucy, Maeve, May, Nina, Paige, Rosa/Rose, Sara(h), Stella, Una, Violet, Zoe.
More unusual middle - is there a family name, first or surname, you could use? Otherwise there are a load of unusual but recognisable girls' names. I like - for example: Aminata, Ariadne, Calista, Cordelia, Cornelia, Evadne, Felicity, Geneva, Genevieve, Ingrid, Isleta, Ismene, Jocelyn, Mariana, Marina, Rosalia, Rosario, Serena.