I had an issue yesterday. My son has a glider, my son is 18. After a month the sugar glider trusted him and they had the most wonderful relationship. We took her to the vet because we thought it was a boy and he needed to be neuter since we just got a girl to keep him company. When we got there the doctor said it was a girl, so we didn't need to neuter her. When the doctor try to take her out of the cage the glider's head got stuck in the cage bars and she was screaming and crying. The vet took her by force through the bars and she was crying and biting. Now she is home and wont get close to my son or anyone. She is in her pouch and wont even come close for treats. I feel awful! Since it was my idea to take her to that place. I left a treat in her pouch and she ate this morning, but inside her pouch. I haven't put the 2 sugargliders together because since she is afraid I don't know how she will react. PLEASE ADVISE!!! I am desperate

Honestly, the best thing to do is give her time. Try to watch her and make sure she’s not hurt from the vet. I do not think you broke her trust, I think she’s just scared about getting hurt/mishandled again and once she feels safe again, she’ll be fine.
For the introducing the two together, sugar glider are territorial so they will have to get used to each other before they can live together. (The younger the are, the easier). Switch out their sleeping pouches with each other’s every night, so they can get used to the smell. Also, let them out to play together in a safe area, such as the bathroom or tub where they can’t run away. Make sure you supervise them during this just in case they try to fight with each other and you can easily break it up.

like Savannahhhhh said, give her some time. Maybe you could try to hold her in the pouch but dont stick your hand in there, just hold her and try to make her feel safe. Also maybe get her a new vet, and just to be sure, check if she has a pouch. that is a telltale sign of it being a female. she doesnt sound like a good vet if she wasnt gentle with your baby