There are many reasons why a dog can fail to cope when left alone. It is important that this is looked into in detail so the right diagnosis and advice can be given.
Behaviourist Claire Arrowsmith says:
A professional behaviourist will be able to look at your routine and video what is happening so you can respond appropriately. You will probably have to look at how attached your dog is to you; is your dog able to cope in one area of the home while you move into another, or does he need to be where you are at all times?
Is your dog worried by any particular noises or events within the home that could be making him less confident in being able to cope when you are not around?
Having a secure sleeping area is helpful as long as he is used to going to this place to relax when you are around too. An Adaptil diffuser or collar would be a better option than the spray as this has to be applied at a specific time before you leave, and will only last for a short period.
How long is he left for, and whether her agitation begins as soon as you leave are important in understanding this problem.
You may have to get her used to having short periods where she cannot have attention or fuss from you. Then teach her to tolerate short sessions where you leave the room and then the house, building up to normal excursions.
In the short term ask a family member, friend, or professional dog sitter to care for her, because every time she howls in distress the problem becomes compounded and more difficult to address.