All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we ask Allaah to facilitate your matter and grant you this baby, bless him/her and make him/her a comfort to your eyes.
As regards the clothes for new-born babies, then they are often the same for both males and females, so it is permissible for you to dress you baby in any of these clothes.
However, when a girl reaches the age of puberty, it is an obligation upon her to wear Hijab; Allaah Says ordering the pubescent female believers (what means): {… and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their head covers over their chests.}[Quran 24:31]
Similarly, if she reaches an age at which she can be desired by men, then her guardian should oblige her to wear Hijab as a way of repelling affliction. This differs between different girls; a girl may be physically very big while she is only seven years old.
As regards your infant, she is not subject to the rulings on ‘Awrah at this age, and it is permissible to dress a young girl who is below the age of seven, in clothes that do not cover the arms or legs.
Allaah Knows best.