Hi there,
I don't think you mentioned the consistency of her stools? If they are not hard, don't worry about it, or try not to. :) My little guy is almost 11 months old, and has gone up to 9 days without pooping! I've taken him to the pediatrician several times, but he was happy and she examined him and said he looked great. I even got a second opinion and that pediatrician said no to worry either. One of them suggested that since I breastfeed on demand, and often, that he wasn't eating enough to need to poop frequently. Since he's now eating more, he's pooping a bit more often, but he just went 4 days and he's been eating a lot.
Try not to worry as long as she seems comfortable, and as long as her stools are not hard. If she is constipated, with hard stools, then you need to do something. My daughter (now 4 yrs.) had a horrible problem with constipation. It lasted for years and was excruciating for her. But that was probably from an allergy that made pooping painful, so she held her stools, making them harder, and it took forever to break that vicious cycle.
If her stools are hard, you can try Miralax when she's old enough. I don't know at what age it's recommended. If they are not hard, try to relax and trust that her little body will work it out. :)
Also, we just found that watermelon has quite a speedy effect on our little guy. But seems like every kid has something different that works.
Good luck!