A feminine form of Ethelbert, which is itself the Middle English variant of Æþelbeorht, which is in turn the Old English version of Albert, Ethelberta could therefore be regarded as an alternative form of Alberta. 
 
Ethelberta certainly has plenty of clunkiness but nicknames Effie, Bertie, Birdie or Ella might lighten it.
 
Ethelberta appears in Thomas Hardy's (surprisingly comic and happy) novel, The Hand of Ethelberta, about a woman of humble origins who marries well, loses her husband, and becomes a poet and story teller, all while trying to support and conceal her working class family.

Ethelberta

Ethelberta Origin and Meaning