My son names [name]AARON[/name], needs name for his sister. begin with any letter. Thanks.
[name]Aaron[/name] is incredibly handsome! For a sister, I’m thinking another Biblical name might be nice…
[name]Eva[/name]
[name]Julia[/name]
[name]Rebecca[/name]
[name]Susanna[/name]
[name]Elizabeth[/name]
or
[name]Charlotte[/name]
[name]Violet[/name]
[name]Anneliese[/name] (although an A name could set you up with an A theme for future children)
[name]Abigail[/name] came to mind. [name]Aaron[/name] and [name]Abby[/name] would be sweet together.
Another vote for [name]Abigail[/name] nn [name]Abby[/name].
E names game to mind.
[name]Aaron[/name] and…
[name]Eliza[/name]
[name]Eloise[/name]
[name]Emmeline[/name]
[name]Elena[/name]
I know a sibset [name]Aaron[/name] and [name]Victoria[/name]. I think the two names flow well together. I also like [name]Aaron[/name] and [name]Abigail[/name] because they’re both biblical names and both start with an A. 
I like [name]Miriam[/name] with [name]Aaron[/name]. They were siblings in the Bible too, and while I think that’s awesome, it may be too much for you on the Bible theme.
[name]Aaron[/name] can mean mountain. [name]Bryn[/name] means something similar, which could be a nice link between the two. They have different origins, but a similar feel.
It would help if we knew what kind of girls’ names you like, but here are some ideas:
[name]Lucy[/name], [name]Jane[/name], [name]Mila[/name], [name]Audra[/name], [name]Emma[/name], [name]Cora[/name]
Other double vowel names
[name]Fiona[/name]
[name]Amelia[/name]
[name]Abigail[/name]
[name]Noelle[/name]
[name]Olivia[/name]
[name]Paige[/name]
[name]Violet[/name]
[name]Zoe[/name]
[name]Laurel[/name]
[name]Naomi[/name]
[name]Chloe[/name]
Other simple classy names:
[name]Anna[/name]
[name]Holly[/name]
[name]Clara[/name]
[name]Jane[/name]
[name]Rachel[/name]
[name]Eve[/name]
[name]Aaron[/name] and sister…
[name]Rachel[/name]
[name]Leah[/name]
[name]Cecily[/name]
[name]Zoe[/name]
[name]Hannah[/name]
[name]Lucy[/name]/[name]Lucille[/name]
[name]Josephine[/name]
[name]Phoebe[/name]
[name]Lilith[/name]
[name]Harriet[/name]
[name]Celia[/name]
[name]Chloe[/name]
[name]Georgia[/name]
[name]Lydia[/name]
[name]Ruth[/name]
[name]Naomi[/name]
[name]Dinah[/name]
[name]Stella[/name]
[name]Claudia[/name]
[name]Sophie[/name]
[name]Sadie[/name]
[name]Meredith[/name]
[name]Ruby[/name]
[name]Aaron[/name] was my parents’ name for me if I was a boy! So how about [name]Rachel[/name]?
others: [name]Sarah[/name], [name]Leah[/name], [name]Eden[/name], [name]Amelia[/name], [name]Amalia[/name], [name]Lena[/name], [name]Aviva[/name], [name]Morgan[/name], [name]Payton[/name], [name]Stella[/name], [name]Shayna[/name]