I am a normal healthy woman with a 2 year old, and have slept until 11:00 when she has slept that late. It's not unusual for mothers of young ones to need to get caught up on sleep.
When there is another adult around (in this case the grandma), I can see a mother sleeping undisturbed. When my husband is home, I've slept right through them getting ready to go out and then leaving, not even realizing they've left and come back.
I do wake up very easily to any crying or distress though. Sleeping late doesn't make a person a bad mother, it just might be her routine that works for her and her family.
Please come home safe Tyler.