She very well could be pregnant. Around 4 weeks of development in the pouch, is when you start seeing the lump(s) which is the little joey(s). So yes it does take about a month before you can visually see that she is pregnant.
Do not try to look into the pouch because because if she is, the baby can be dislodged from the nibble and be unable to attach itself again.
Do a search on pregnant gliders and joey rejection.
Also look at
www.suzsugargliders.com/breedingsugargliders.htm
along with the whole Suz Sugar Glider site in general because their is more information then just the info on breeding. Great into on joeys, development, etc.
And I would recommend getting a joey rejection kit and uping her protein for health and milk production. What diet are you using?