This is usually caused by gall stones. My guess is the pain appears during the evenings because she has had a large main meal.
She needs to eat smaller meals - not necessarily less food but small amounts more frequently, cut out fatty and acidic foods and try and move about after meals to aid digestion.
I can sympathize here having had the same problem it is very painful. It is generally recognised that fatty food can set off the painful episodes but it doesn't always work like that I'm afraid. One of my worst times came after I had eaten an apple! As ethel says it is usually caused by gallstones - has your GP suggested a scan to see if that is the problem? If it is then surgery is often the best way out - it is done by keyhole surgery normally. It certainly made a difference to me.
Thanks so far. She dosen't drink, has learnt to eat small amounts, we watch fat intake as she has high cholestral, and yes, the scan has been requested. Please continue with your imput.