I agree totally with the above postings.
Tell Mum to get her levels done every 6 weeks until her levels are stable.
It may not be a side effect of the med. It may be an effect of not having enough med.
Do you know if she's been tested for TSH, FT3, FT4?
She should be retested now anyway, and her meds should be adjusted. TSH target is usually 1 - 2. FT3 and FT4 target are usually middle to upper half of the reference range.
Read up on Hypothyroid. This should also explain your Mom's symptoms.
Hope this helps.
Best wishes
I am not an expert but I would think that she needs a higher dosage of levothyroxine because all of those symptoms you wrote she has are of being hypo. She should have her hormone levels retested. Good luck to you both.
And the medicine probably has some side effects but I never bothered looking into it because I'd rather not know. But, that's just me.