If you can pick up her feet without her fighting you, then a good farrier will be able to take his time and get her trimmed. With horses like her who are out of shape or injured or old and can't hold a foot up for extended periods of time, sometimes you just have to pick it up, trim a bit, and set it down before the horse gets too tired to hold it and tries to take it away.
Where most folks run into problems with that is you need a farrier who is also a horseman so he can recognize when the horse has had enough and can stop before going too far and creating a training issue.
If you can't get her to stand without fighting, then what I would do is work on her training before calling a farrier. She's been without hoof care for over 3 years, I doubt if another few weeks are going to cause permanent damage...but drugging her and/or having her fight could.