That Starcraft XP 18RB has a GVWR 3500# and has 10" electric brakes so therefore the brakes are for stopping the trailer and S?B functional when connected to tow vehicle via 7 pin umbilical cord.
Emergency braking would be in addition to normal braking function.
Emergency braking when pin gets pulled ....trailer battery then supplies DC Voltage to trailer brakes otherwise with pin inserted DC Voltage for trailer brakes would be supplied via tow vehicle brake controller
If trailer brakes didn't work when connected to truck then they are not going to work in an 'emergency' when pin is pulled...same wiring/braking system
Trailer brakes could be way out of adjustment, worn-out, broken wiring, bad magnets etc
But your brake controller should have acknowledged trailer brakes....something is wrong