I'm sorry to hear things are rough. It is sad that your lo's gma is disrespecting your wishes. It really shouldn't be about her, but about the baby....but we already know that, right?
Perhaps try this: Tell her that the **DOCTOR** said to ease up on solids and give milkies when baby needs it. Lots of these old-fashioned stubborn types will listen to the doc, if no one else. Good luck!