Personally, I don't think pre clearance is a good idea as they may easily deny you boarding your flight, since you will still be home in Ireland it may be easier for them to tell you to start the journey afresh by reapplying for your green card immigration process. Hop in a plane, don't panic, do not surrender your card while here, get all necessary documents regarding your mom's health and in case you get an NTA, you will show the immigration judge so you can get a favorable outcome.