Hi I don't know enough about your situation to say but just some questions, I would ask myself
I would not want her to ruin Christmas for your kids-
Do you think she would? has she kept up any r with the step kids? Would it be a positive interaction on Christmas? Are there any other motives? Is she clean and sober or addicted?
if you think it would be a positive experience--trust your gut if you think it would be a fiasco -be cautious- look into your motives-
married 14 years H 42 bomb 2/07 IDLYA D final 3 /09 M ow D ow