The capsules CAN work, but not effectively as the oil. And when the oil is used correctly, she won't have ANY high/euphoric feelings, and she can easily go about her normal day without pain, and without high feelings.
For pain, a high CBD strain and lower THC strain would be most effective.
Edibles and vaping are great for the times when the added relaxation of a high is needed, especially bed time with a strong Indica. Nothing could help her sleep better.
During day time using a Sativa oil, she won't feel any high, but a lot of folks DO feel the extra energy boost from the Sativa, and that works great when there are errands to run, or chores to do. If she was using an Indica oil, it will help her sleep, without the high feelings.