A few random thoughts/suggestions:
1) That sounds like a lot of change. Maybe she just needs to go back to the basics with loading into and riding in the trailer – some time with you just walking into and out of the trailer at her own pace, and not for an actual trip somewhere.
2) Could she be having pain going uphill on the ramp / stepping up into the trailer? Maybe try walking her up a steep hill to see if she moves freely up it or acts like she’s in pain.
3) If it’s anticipation of pain, as someone suggested, or nervousness due to multiple changes in her lifestyle, it might be beneficial to use a calming supplement (like SmartCalm paste) for a few trailer rides to calm her down enough to realize that she’s ok.