The thalamus is a very important part of the brain, and a stroke there can be quite debilitating.
First, with regard to the limb pain, this is very common after
a thalamic stroke. It is similar to the phantom limb pain people complain about after a limb amputation - the body simply doesn't know how to interpret a lesion in the sensory neurons coming from the limb through the thalamus, and mis-interprets this as pain. In my experience, it is best treated with the medicines amitriptyline, nortriptyline, gabapentin, Lyrica, or possibly Cymbalta.
The headaches may also be from the stroke, and a headache disorder which started because of the stroke, and the above mentioned medications can be very helpful. Topiramate is another effective headache medicine, but you might find that it makes her speech problems a bit worse. I strongly agree with your doctors, however, on the need for a angiogram and a spinal tap - to make sure that there is nothing else at work, such as an autoimmune attack against the brain or the vessels in the brain.
The difficulty with speech is not uncommonly seen after a left thalamic stroke. It should improve slowly over time. Usually, the most improvements are seen over the first 3-6 months, and come very slowly.