Answers to questions asked.
1. Does she have bad ground manners? In my opinion, No. She is very respectful when being handled. Follows you like a dog without any hands on the lead rope. She will stand ground tied for an unlimited amount of time. She will stand while being saddled (Ground tied or someone holding her). She responds to all cues when being ridden or worked on the ground (Lunging).
2. Does she act "Freaky" when more than one person handles her? Myself I have tried to give shots and have had the same problems when two people handle her.
3. Is she scared of needles? I don't know... I would guess so. You can approach her with a needle showing, but once you start to try to insert the needle to medicate, she FREAKS!
Okay, so she just has an injection phobia. Sounds like my daughter when she was 3, lol. But seriously, I would agree with tranquilizing her orally BEFORE she becomes upset. Ask your vet about dosage, but generally you can give Ace by mouth double the IV or IM dose, which usually works out to 3-5 CCs. At least, that's the dosage I have given to my horses orally before. If she gets scared with a needless syringe, then squirt your dose into a handful of feed or inject some apple pieces. You might want to add a CC, just incase she drools any of it out, lol. Confirm all of this with your vet of course.
So, then go about grooming her or whatever until the Ace has taken FULL effect (20-30 minutes). You want her sleepy looking, but not falling over. When she's nice and sleepy, have someone distract her by brushing her neck. Go to her haunches with the needle hidden and turn your back to her. Rub her hip with your free hand, then pinch the skin a few times between your fingers. Time your needle stick with a pinch. Be sure to plunge as you poke and stay light on your feet so you can jump out of the way! I would do all of this OUTSIDE with the mare untied. You don't want her to back anyone into a corner or break a cross tie.
I would suggest having your vet do all of this though. Your vet will have more experience in timing a poke and being able to get out of the way. Tell the vet that you want this to be a training exercise as well, so the mare can start getting over her fear. Ask the vet to explain to you what he/she is doing, so you can try it yourself next time.
Also, I would ask your vet if he can use a topical numbing agent, Maybe if the horse doesn't feel the poke so much, she won't freak out. ?