I don't want to sound too strong on this one. She could have had a bad day, been overwhelmed on that day, had a setback, forgot to take her anxiety meds, was just completely freaked out by snow and didn't think her boys could support her in a power outage or whatever.....

BUT... You have been very agreeable to adjusting your schedule to her wants/needs, and around her younger son. You've agreed to wait to merge households.

Blending lives means blending the responsibilities in each others' lives. You're working with her for her responsibilities. YOU have responsibilities too.

If you gently remind her that this is the case, that you have someone else you have responsibilities to, just watch for her response and give it some time. This may be a growing moment for her in this relationship.