Lung her one her non liked side
Spend a bunch of time on her bad side! Also try to build up her confidence going whichever way she doesn't like
what i have done is stretch them to their bad side before a ride by using treats and having them touch their own side with their nose. i also have done lots of circles and different exercises on her bad side first at the walk, then trot, then canter and this has helped my horse a lot to not only feel more comfortable on her bad side. it also be better at getting her bad lead
try to do small cercles on the bad side
You might need to spend a bit more time on her weaker side to strengthen it up, horses like people naturally have a stronger and weaker side just it can be more prominent in some. Using more precise and exaggerated aids will help but lots of bending will help. So if you're in arena with markers try small circles as you go along. Every 3rd marker do a 10/15m circle. Using a schooling whip to tap the weaker hind leg can help them to track it up, but I've also read about a sausage band that goes around the weak hind fetlock. This makes them more conscious of it and more likely to pick it up! Hope this helps, sorry it's long
What has helped me is serpentines (idk english, the s shapes). It helps your horse to bend to both sides and be softer and listen more.