That wound isn't that bad and in my opinion probably didn't even need stitches. The only time neck wounds typically need stitches is if the wound is large large (usually large because the glider didn't get separated early enough so it went from a small dime size to a 50 cent piece size)
Having said that if it's your first neck wound they do kinda freak ya out and think it's worse than it actually is
The vet is correct to not use an e collar, it's not necessary for neck wounds and would only irritate it further. The meds he gave are widely used for gliders.
Def keep her separated until completely healed. She may not eat as much as usual and may lose a gram or two during her recovery but that is normal.
Normally I would suggest using vetericyn vf on the wound but the vet probably used dissolving stitches so just do your best to keep the wound clean and the hair surrounding it smoothed back so it doesn't get gunked up in the scabbing if there is any, it looks like they shaved a good size patch so that will be a little harder once it starts growing out again ....... if need be you can put some neosporin ORIGINAL formal NOT the kind with pain relief in it then smooth the hair back away from the wound.
Putting her back with the pair is totally up to you, we can't tell you it won't happen again nor can we guess that it will either. Sometimes they do and sometimes they don't...
I've had two separate gliders with neck wounds that didn't regrow hair at the wound site. Those two gliders I re paired because I felt their bald spots would make them even more of a target for another wound. I've had some that the hair grew back and they went back in with their colony and never got another one and I had one that did get another one so he was re paired once healed. It really comes down to knowing you will need to monitor your gliders and hope it doesn't happen again but prepared in case it does.
Wounds of this size usually take about 3-4 weeks to heal give or take a week or so I hope she recovers well for you