As already stated several times, Catholic funeral Masses are not as complex as a Wedding Mass. The Parish can either handle everything or cue the persons chosen to give readings, bring up gifts, etc.
It's not expensive. It's not inconvenient. It's not time-consuming. It's not a major burden in terms of actions and responsibilities.
Most of the family was Catholic at some point and the sister is still active in her own parish. The MIL is a Catholic and this is what she's asked for at the end of her life. The woman is still alive, has some assets and a small insurance policy, so she's not the financial burden the OP is trying to paint.
There's really no excuse for denying the woman what many Catholics consider to be a final blessing and send-off. As already stated, a Catholic funeral is NOT a sacrament, but it is a respectful and prayerful farewell blessing that many feel helps their souls ascend into Heaven.
Cheap out on the flowers, the visitation/wake, even the hospitality, but don't cheat the woman out of her funeral Mass in Church.
Well, I definitely agree with you on that. I am just pointing out that for non-Catholics sitting through a Mass is not a comfortable thing. Nevertheless, if these are the woman's last wishes (and I know she is still alive) I would do my best to see them followed if this was my family member.