To be honest if you are that worried try something else before going out with this combination.
Take the mare out with another reliable horse just to check that she is not crazy with food/the noisy woods. Go out on a quieter time, depending on where you are early Sunday morning may be a better bet than this close to traffic chaos. Then try her out in the school with the polo pony to make sure there is no squealing and kicking out.
Remember to wear good hi-viz and carry a mobile. Good luck!
From previous threads some of you may know that I help look after 2 horses of a crazy friend , who was going to loan one horse but then ended up owning three in less than a year. After a tough winter of helping look after them in a muddy field with no rides and constant frustrations of her not having enough knowledge to understand their needs, we are now at a yard with a school and all is well. We have bought one back into work and this afternoon we will be going on a hack . She will ride the ex polo pony and I will be riding another horse that i poo pick (and throw wine at the owner)occasionally in exchange for rides, she is a 21 year old welsh cob who i have ridden on and off since she was 7 so i like to think she is fairly reliable . Can we have some good vibes, just a bit nervous as 1. i dont know how my horse will react to a new hacking companion she can be a bit mareish 2. There is tree felling in the woods and heavy noisey machinery but we cant avoid hacking for 3 weeks . 3. My horse has lost weight recently so now has a lot more food than before so i worry she will be crazy . 4. We have to go on a road and after reading all the posts on some horsey facebook groups about drivers being downright malicious around horses im convinced we will meet one- although friend is a police officer so hope she will gallop after them and arrest them .
And breathe! So yes good confidence giving vibes please especially between 4-5 pm as thats when we are going out