Hi,
Propanolol can have some effect on the conversion of thyroid hormones and as such MAY have a small effect on TSH(one can only wait and see what effect it has on your wife specifically, especially at this small dose). That said, I strongly urge you NOT to acutely stop taking the propanolol without discussing it with your wife's neurologist. If this medication is thought to be the best for her neurological situation then adjustments can be made to her thyroid medications to keep her TSH in goal range. This case may be complicated in that the neurologists may want your wife' s TSH at a higher level because of her stroke history, so all specialists need to communicate especially well about this to avoid misunderstandings.
All the best.