I'm sorry but I'm confused. You said you got your puppy when she was 6 weeks old but that she's only one month old now.
I don't have any other advice than that which has already been given. The grated parmesan cheese worked well for my Lulu (but she was 14 weeks when I got her). I just sprinkled it on her dry kibble & she began to eat. I only do it now as a special treat since she eats her kibble well.
If your baby is already 2.5 lbs at one month old or even 2 months old, she will more than likely be larger than 5 lbs. The rule of thumb is to triple the 8 week weight or double the 12 week weight...but that's only a guesstimate & is not always accurate.