Not every person responds to the same treatment regimen and sometimes even in the same person it can change over time as there are many factors influencing blood pressure.
If it seems to be consistently high for several days then her regimen should be changed either by incrementing dose or by introducing another antihypertensive drug of a different class. I suppose you have been told about the need of a low salt diet. If the patient has other symptoms apart from the measurings like intense headache, confusion, vomiting perhaps more urgent evaluation and treatment in the emergency department is more appropriate.