Merkle's recent tremors point to a neurological disorder such as Parkinson's disease.
The tremors of Parkinson's are more noticeable at rest. People with Parkinson's watch their hands shake when they rest in their lap. But when they reach out to grab or hold something, such as a cup of coffee, the shaking stops.
I think this explains why Merkle holds her fingertips together. If she presses them together the muscles are active and won't shake. If you watch the most recent video of her shaking, she is either holding her hands together or her arms.
I think she's had symptoms for years and we just haven't noticed. Runs in the family as Hitler also had Parkinson's. There is video of him shaking too.