Brief Answer:
Actually accutane most common side effects include joint stiffness and yes her thyroid can cause theses symptoms that you have mentioned in your given history .

Detailed Answer:
Hi i am Dr Ahmed Aly
thanks for using HealthcareMagic site ,
I had gone through your question and understand your concerns ..

I hope your daughter feel better soon , you mentioned she taking accutane which actually causes bone , joint pain and difficulty of movement which may be shown as stiffness .( these are common side effects )
If she have a history of thyroid diseases may cause hoarseness of voice , dizziness and stiffness as thyroid hormone abnormalities affect the muscular tissues and cause muscle weakness or what is called myopathy .
Hypothyroidism or low throxine hormone levels affect joints by many ways like weakness ,cramps , stiffness , arthropathy ( joint pain ) , tendinitis , tarsal tunnel syndrome , frozen shoulder etc . While hyperthyroidism affect muscles more often by causing myopathies like difficult swallowing , hoarseness and difficult climbing stairs .
I think she needs to stop accutane or take an alternative and manage her thyroid profile with her physician or specialist for proper evaluation and management .
For now she may take muscle relaxants and use hot gentle massaging with topical anti-inflammatory gels and she will be fine .

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Any further clarifications feel free to ask.

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