It all depends why she was out work. Was it injury related? If yes what type of injury? My mare has been off for 3 months due to suspensory ligament issue and I've been advised to NOT lundge in circles but ride in straight lines only....first week only walk so she gets used to weight on back then slowly build up
Lunge for a few weeks a bit of gentle hacking on roads if it's an option and timr
Maybe just troting, trotting will help her get fitter
Start out slowly, she would have lot alot of muscle tone meaning she can be very prone to injury. Start at a hack at a walk for maybe one week and at the end of that week you could add some trot. Then progress to more trot etc. Take it slowly and be in tune with how she feels.