[Dr.Brian]

Blood clots are fairly common with birth control pills. However usually they are treated, not sent home. If she had a transient ischemic attack (TIA) she's at risk for another. Did she stop the pills and start some kind of blood thinner?
The other likely possibility would be an irregular heart rhythm that made her light headed and short of breath. That could spontaneously resolve with no evidence it occurred. If it happens again, have her, or you, feel her pulse in the artery in her wrist or neck. See if it is very fast (beats per minute) or irregular.
Unfortunately there's little you can do if she doesn't want to take care of herself. If she wants to ignore symptoms that might suggest a potentially life threatening problem, she's quite literally gambling with her life. There's a reason Russian Roulette isn't very popular. Bad things happen to healthy or young people. Someone is going to be the 1 in 1 million. Hopefully it's not her.
Good luck.