L.P.
If you are only fostering this child (which I am not minimizing by any means - it's a WONDERFUL thing you're doing), I just don't understand why you'd want to change her name? And I don't understand why you'd be allowed to change her name, being a foster parent, not a bio or adoptive parent? Even if, as a foster parent, you're her legal guardian, I still don't understand why you'd be allowed to change her name...
In any case, best wishes to you. How blessed this little girl is to have someone to love her in her first months of life. Best wishes.