Ohhhh that excitement of a new horse friend! Do a few days of groundwork. This means seeing their reaction to everything new to them, what they think of blanketing, how they handle grooming, do they like their ears touched... these will give you an idea as to how they react to stresses in their environment and how quickly they turn to or away from you when they feel insecure. If all good to go then lunging should not be a problem provided you do everything step by step. If that's good to go then you ride them in a controlled environment and check all the basics and again reaction. Progress to hacking out. By now you will have a good idea whether the basics are in place and you don't have to do any additional "trust" schooling or maybe you will find A grey area/gap in schooling which you can smooth over. This will create a two way bond and there won't be surprises and whatever you do after that you will know if to trust/calm her or be the leader. This can take days or months. Enjoy your new friend 🙂
It takes time. Definitely be kind and use the right bits and tack so your horse doesn't get the wrong impression. Also, gain trust by trusting your horse and not being to nice but not to strict. you still need to establish discipline but reward your horse when he/she doesn't something correct. Also use proper aids so you don't confuse your horse. Also, give treats!
Join up does wonders tbh and also lots of ground work. Ride tackless and get to know her personality just by being with her so that you know what to expect if anything happens. Honestly the more time you spend with her the more you learn to trust each other. Do some trust exercises like riding without reins, ground work (in halter) riding in halter, riding tackless, etc. just suggestions :)