Welcome to the forum.
Your new gliders are just settling into their new home. EVERYTHING is strange and unfamiliar to them - they have lost their parents and everything around them smells strange to them.
Give her some time to adjust to your home and she will probably move to one of the pouches soon.
I would not leave an entire shirt in the glider cage. The seams on most clothing are not glider safe. The long overcast stitches are too loose and can snag a glider's nail or even a toe and cause injury if a glider struggles to free herself.
Instead, get some fleece and either tuck a few 3 or 4 inch squares in your clothing for several hours or sleep with them in your pillowcase overnight to get your scent on the fleece. These can then be tucked into the sleeping pouch to help your glider get familiar with your scent. You could put one of the pouches on the floor of the cage for the joey to crawl into if she is not yet used to a hanging pouch. Once she is in the pouch then you can just hang it up - she will catch on quickly especially if the other glider joins her in the pouch and they can snuggle together.