The name Berta for a Girl?

If we have a little girl he name will be Berta. (I'm not asking peoples opinions on the name, so please if you have negative comments I don't need to hear them) Berta is a family name and would be named after my wonderful Grandmother. It is said with a soft T and makes more of a D sound. It almost sounds like Britta pronounced wrong when you hear it (Britta is also a beautiful name so if she ever accidentally get's called Britta I dont think that it would be problem). But the question I have is with the spelling. I would love to keep it Berta because that is how the name is actually spelled and I would like to stick with the traditional spelling, but does it look too harsh? Would Berda or some other spelling make more sense and make it look a little more feminine? Or does it make the name look like Brenda? I really wouldn't like to change it but if it would help when people are reading the name, it might save her from a life of having to re-pronounce her name all the time. Her nickname would most likely be Bertie, said like Birdie so should we maybe stick with the traditional spelling for the full name and then have a D in the nickname? Thoughts? Or am I picking this name apart too much?