Like others have said, there really isn't no 'real' perfect time to take baby pictures because it's always a good time! We just had our first little one and she is 3 weeks old and every day it seems like something has slightly changed on her. Within the first week of being born, that is the lowest weight the baby will ever be, and will typically gain up to 1/2 ounce a day and by one week be at their birth weight.
Also, babies will eat every 2-3 hours, so see if your friend has a feeding schedule that they stick to, so she can travel after the baby feeds. But this will also give you roughly a time line of what 'moods' the baby will be in. My little one after a feeding is in a 'milk coma' and I can pose her any way I want without her fussing.
And as far as travel, that is up to momma and baby. My wife went to Target by herself 3 days after having our little one and we traveled to my parents (45 mins away) the very next weekend. My sister who had her baby a month ago, left for the first time (going to my parents as well). So every situation is different. I know you have the stuff at your studio, but doing the shoot at their home will make those pictures even more unique and special to them because that's the house when 'baby' came home. It's kind of depressing seeing babies in the same bucket with the same background. Cute yes, Original no. Plus being at the home is more comfortable for momma and baby and may get more 'natural' emotion.