Delta is the fourth letter of the Greek alphabet (and part of many a sorority and/or fraternity name). It's also the name of the land around the mouth of a river. It hasn't been very popular here in the U.S. since the early 20th century, when it last hit the top 1000, but with all the Ella/Elle names in vogue, this feels like a natural variant.
And Bell, obviously, is in honor of Mom's surname. Together, it has a bit of Southern flair. You can picture a Gone With the Wind character named Delta Bell(e), can't you?
What do you think of Kristen and Dax's pick? Is Delta destined to reenter the top 1000?