She might have a urinary tract infection.
She might need to urinate more because she is at the point in her heat she is ready to breed and spreading those pheromones in the urine is instinctual behavior.
Don't let her out alone even in a fenced yard as if a male gets in to try and breed her she might get hurt if its bigger and she might get bred if it wasn't too much bigger.
They will seek a mate out if possible and that might be part of the whining to going outside too.
If this keeps up once her heat is over or if you see blood or pus in her urine then see your vet for diagnosis and care.
Hope this helps you!
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