I was actually in the same situation as you. My husband is from S. Africa and some relatives from there wanted to visit around the time my third was born. It didn't end up happening but I was very concerned. Every well baby visit the doctor asks if we or any close relatives have been out of the country. They are asking this because of tuberculosis. My husband was actually treated for being "exposed" to TB sometime while he lived there or traveled. There are sooo...many sicknesses that one can get just being on an airplane. I would definetly wait at least a few weeks maybe longer. Your ped may say "oh, don't worry about it" but use your own judgement. I would be just as concerned if it were any other country.
Breastfeeding does help but let me tell you from experience that it doesn't protect against everything. My 8 week old son caught a bug and actually was hospitalized even though he was exclusively breastfed. I personally wouldn't rely on breastfeeding to keep your child free from sicknesses, although like I said nursing helps.
Talk to your doctor and see what he/she says. There may be a certain time frame that is recommended. Good luck to you and I thought I would respond since I have been in this situation before. SOme may think this suggestion is crazy but maybe she can wear a mask and limit her time around the baby?? Just an extra precaution if she can't wait to see the baby.?? Also, I see you also have 2 other children that could "catch" something and you could too. Having a new baby is stressful enough that the last thing you want to worry about is all 4 of you catching something...or she can even be a carrier of some diseases. I'm sure their is some sort of incubation period so ask your doc.
Sorry so long! Good luck and let us know what your doc says.