I think the most important factor is the kind of caregiver and parent your mother is. If she provides high-quality, enriching, loving care to your child, then you should consider leaving. If she doesn't, the question has been answered.

People love to tell you that time with your kids is precious, and it is. Security is also very precious. If you are working all the time and you are financially insecure, then you have created a very bad life for your child. I think that you can take the overseas job if it substantially increases your security AND you have a very good living situation for her.