I agree. Healthy relationships require some level of balance. Making the relationship in your own image at the expense of a partner is not considerate and at worst, a controlling behavior.
Jill and/or Bella should be involved in MC's wider social circle, where appropriate. For Jill, this is a source of drama given how things went with Rusty. For Bella, professional distance from students seems fitting regarding the party, but would not preclude her from participating in other activities, such as the nursing home or other projects DIKs may have.