I wouldn't bring it up to MB. Just make yourself busy. Plan outings for every day of the week. If she asks when she can come over, just say, "Oh, now that the holidays are over, we are back into the swing of things--busy every day! But you can meet us at X park on Friday between 10-12, or at Y museum on Tuesday from 10-11. Maybe we'll see you there!"
That way, you aren't trapped in the house with her, and you don't have to engage as much because your charges will need actual supervision. With my charges, we are out every morning and afternoons we run errands, fold laundry, wash dishes, make dinner, do baths, etc. If you are similar, then afternoons are booked with chores, and mornings are out. She can join you for a fun, age-appropriate (for your charges at least) activity once a week or so just to keep a connection between the kids, but it doesn't have to be a bonding experience for you.