Hello LJ,
I've been on Tasigna now for 3.5 years. I find a 10AM/10PM schedule works quite well for me. As for the 12 hours, Sandy's advice is spot on - consistency is better to maintain the plasma level. In fairness, my routine often ends up with about an hour variation i.e. 9.30AM and 10.30 PM ish.
As for the fasting, i try and stick to the 2hours after food and 1hr before food as strictly as possible; however, 20-30 mins after taking my tablets I will happily drink tea (with a half teaspoon of sugar) inside the hour. My advice is to avoid consuming anything with significant calorific value inside the hour after taking the meds - milk or cola would be a bad choice.
I do find that Tasigna can mess with my blood sugar levels and consequently I get ravenously hungry after taking the tablets - a cup of tea does help alleviate this. Once your mum gets into the rhythm it will be quite easy - I work full time and it fits into my day just fine.
I think it's the same on gleevec but stay away from grapefruit or grapefruit juice.
Happy to answer any more Qs you may have.
Chris