I would suggest trying to find an open stock trailer you can rent or borrow... then some stock pannels to create a chute for her. For now.
Once you get her home, then take a look at some different trainers and see what seems like it'll fit you, your new horse, and your situation.
If you can't handle this filly you won't be able to load her like a "tame" horse - so I wouldn't even try at this point, you'll only create more fear in her unless you can take the time where she is right now to gentle her and get her used to simple handling and leading.
Loading into a trailer is a real trust game - if the horse does not trust you there is no 'stress free' way you're going to get them to load. My personal preference is to never load a horse who is stressed about it - we will take as long as it takes to get the horse to realize there's nothing to fear and walk in on it's own.
I have, however, loaded into an open stock trailer by means of a chute, in order to remove a horse from a really bad situation - a few times. We didn't have the time to gentle the horse where it was (and in more than one case they didn't have a safe environment to try even if we did have time). I wouldn't do it in a straight haul though - they aren't really designed well for it... if I couldn't get a stock, I'd use an angle haul - and just leave the horse loose in the back.