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Whether you should be concerned would be dependent upon the severity of symptoms and whether it can respond to some home interventions.
It is good that you gave her something to eat, but it is also important that she drink some extra fluid to help ease the lightheadedness. It would be good if she were to drink about 3-4 cups of fluids.
If she continues to be significantly lightheaded after the fluids, particularly if it is so bad that she is unsteady on her feet, then that would be concerning and it would be better for her to be seen urgently, regardless of her blood pressure. However, if the extra fluids eases the lightheadedness, then it is less concerning in terms of needing to be seen urgently. However, she may still need to be seen depending upon whether the other symptoms persist.
Nausea that is bothersome for a day or two is most often due to a viral infection, and if it eases spontaneously, then no further evaluation would be needed. However, there are many other conditions that can cause nausea, so if the nausea persists, even if the lightheadedness eases, it would still be better for her to be seen, but it does not need to be done urgently.
So, first see if she can drink fluids and see if the lightheadedness improves, and then whether she needs to be seen would depend upon whether significant symptoms persist.
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