My Mom Is 89 And Takes High Blood Pressure Medicine.

My mom is 89 and takes high blood pressure medicine. She is experiencing dizziness & lightheaded, she feels the need to hang on to things when she walks. She also felt nauseated in the morning and not much of an appetite. She has had to small stokes or TMI's before when she was not consistent with her blood pressure meds. How do I know if this is the onset of another stoke or dehydration from all the heat we are having and she is not drinking much water?
Thank you,