I hear you. My daughter is 10 months old, and she has just started taking milk from a cup or bottle (this week!).
I would suggest trying different kinds of bottles and nipples. You can try everything from something that is supposed to mimic your breast to something that looks more like a sippy cup. Something may work. My daughter likes the new-born nipples that came with my breast pump bottles (uh, Medela), and otherwise she likes normal sippy cups.
Unfortunately, in my case, what finally did the trick is that i went back to work a few weeks ago. Now that she has a nanny feeding her lunch every day, with a bottle before her nap, she seems to be giving in and trying it.
But, it really required me not being there as an alternative, AND, regular effort from her other caretaker.
At 6 1/2 months i don't think she was hungry when you left for three hours. She was probably just cranky. What you may need to do is wait for a regular feeding time, leave, and have your husband try the bottle. Basically every day until you leave, and possibly more than once a day. Its really difficult, especially when you are breast feeding still and thats working!
Good news is, kids don't tend to starve when they have food available - they figure it out after a little while.
Also, leave your MIL with a spoon and a feeding syringe, just in case the bottle is really a no-go for a while.