maybe she just knows that she is going to be a long time without Mummy.
Molly Jane did something similar at that age. so i would tend to agree that it is a separation thing.
I just spent loads of time on the lead up to bed telling her that it was bed time and making sure that she was settled before i left the room. we had a very set pattern before bed so that she got all the cues that it was bed time.
Sometimes it would be over an hour, sometimes more.
I guess it depends what you want to do. We started bringing her in to sleep with us for bad nights, other times i would lay with her until she went to sleep them put her in her cot.
If you are worried that it may be the food, try feeding her earlier.
Mj use to get terrible pain from corn on the cob, or corn kernals...
i took her dinner time back to 4.30pm and bed at 7pm and this helped, slowly i bought her meal times forward so that we now have dinner at about 5.45 or 6pm most night and is still in bed by 7.30ish.

I've just succumbed to it and get up to him, rock him to sleep and go back to bed until the next time.
we did that too... MJ is now sleeping most nights all through the night and goes to sleep most nights after a story and then i leave her awake in her room. it has taken a while, but i have been happy doing it this way, it hasnt been horrific for her (CIO) and although i was tired for a while it was the method i was most comfortable with... MJ knew that if she needed me, cos she was scared, lonely, hungry or in pain i would be there for her.
It might take a while to get throu this phase, but it does ends... its just devestating when you can stop them crying i know....

Have you tried whispering in her ear? i found that sometimes this would help settle her as she would want to know what i was saying... or i would kiss her foot, then leg, then belly, then arms etc etc telling her about it all the time. its worked sometimes (i wouldnt usually do this one in the middle of the night, but sometimes before bed.
Oh another thing i tried was to hold her hand, this worked too at times, i would put her down and hold her hand and sing/read until she was sleep then turn out the light, still holding her hand and once she was asleep i would leave.

Dont know if any of these have helped, i am just writting as i think.
I hinestly kow what you are going through, it does get easier thou