45 yo female feels dizzy on standing.

At the outset one thinks of blood loss. Ectopic pregnancy and dehydration should come to mind. Diarrhea and vomiting as causes of dehydration. Adrenal insufficiency, Labyrinthitis, Carotid sinus hypersensitivity, autonomic dysfunction etc.

She denied any obvious bleeding. That leaves us either with all the other causes of dehydration or internal bleeding.

She did not have diarrhea. (Please note that the candidate asked her if she had  "loose stools" but she didn't understand the term) Therefore please use common American terms like  "diarrhea". I understand that loose stools is an accepted way of asking in other countries but not well understood in the US.

She had not passed urine for a long time. that day. That meant dehydration. One should consider third space bleeding too.

Orthostasis is tested by making the patient stand from lying down position or to make the patient sit up with legs dangling. On looks for a drop in the systolic BP by 10 or racing of the pulse by 20. this signifies a volume loss of about 1 liter.

Hydration is key. A bolus of 500 cc of Normal saline running freely is  appropriate for this hypotension. Observe for improvement   in pulse and blood pressure. Also observe for improvement in urine output. If this does not happen and the patient becomes dyspneic, hold off on a further bolus and consider heart failure. Otherwise, if needed, go on to give another bolus.

The patient improved.

Now you had to review her medications. She took medicines for hypertension. These were "a water pill" (which I hope you know means a diuretic), a beta blocker and was on hormone replacement therapy: You are expected to stop her beta blocker to help her raise a sympathetic response and should also stop the diuretic to allow adequate hydration.  HRT and dehydration - both predispose to DVT. So stop this.

Now before she is discharged from the hospital 2 days later, what medications should she take and which ones should she discontinue?

Typically, before discharge, one is expected to go over medications, diet and activity.

In light of the new findings about HRT (hormone replacement therapy) being more harmful than helpful, you should also ask the patient to stop HRT. If the patient took it with the intention of preventing osteoporosis, one can give the patient Alendronate (Fosamax) or Risedronate (Actonel). If she took it for hot flashes, Clonidine is now the ideal choice as it is helpful in preventing hot flashes and it is also an antihypertensive.

Patient should avoid hot environments to avoid dehydration for a few days and should keep herself well hydrated.