You need to get some exp before going on that mission. Still, there are some things that can make your escape easier:how tf i'm supposed to complete the "Rescue Gray Rat's partner" quest?, getting to Cecily is easy, getting out is impossible
Lure the guards near the door closer to their mines by trowing rocks, then trigger the mines with said rocks. Ideally it will kill 2-3 enemies and damage the rest. Then you can try picking them one by one.
The other trick is to order Gray Rat to block the passage into Cecily cell, and make herself stay inside (cus she is always to die first). Gray Rat is almost unkillable and can kill 3-4 enemies single-handedly before being chipped to death. Meanwhile you can throw rocks from behind to help him a little.