Baby girl 4.5 months old, weights 5.95kg was born 3kg. Is she underweight? She's otherwise healthy and meeting her developmental milestones

No. Sounds normal the average baby doubles their birthweight at about 5-6months which she basically has done.Check with your pediatrician, but she sounds fine.
Normal weight. That is a normal weight for her age. Follow up with your doctor for regular check ups to make sure that she is growing along her own curve in weight, length, and head circumference. How she grows is more important than just the weight at one time.
. Normal weight. Babies usually double birth weigh by 4-5 months of age and your baby seems to be track.