If she is suffering the best Humane thing to do is have her go to sleep in the freezer. It's a tough decision but no creature should suffer in my humble opinion
Seems the post has taken a turn from a mantid likely being gravid to unable to climb or eat, and is now dying. A unfortunate turn of events that seem to have a ulterior issue, rather it be from shipping or the last molt. Age does not seem to be any factor in the issues, but sadly seems the same outcome regardless.
If the mantid is truly dying and is suffering, if you want to euthanize then the freezer is the best method as Kermit suggested. Just leave the mantid in the freezer for at least 24 hours, as I have done less time and had one reawaken from the ordeal.