Okay- I know you think you are helping with this coaxing- with strangers, with being alone etc but the fact is, the dog is receiving this as praise. It may sound strange to you, but the fact is any acknowledgment to these behaviors is only reinforcing them more. As far as strangers coming to the door. Setting up someone to come to the house that is dog savy and will do what you say ahead of time, have them come in the house with you having the dog leashed. The person speaks only to you- level voice- pick a subject and ignore the dog- do not correct the dog or console. Do this several times with at first the same the person, then adding people. When you notice the dog is calm on the leash, try without the leash- but do NOT acknowledge the dog. Tell them not to make eye contact, no one says the dogs name or spell anything ( dogs learn real quick spelling might mean them) so leave the acronyms on the outside of the house..
Second upstairs- crate if you can not watch. The howling - ignore.. I know it sounds awful- howling is a form of sorrow- so either do not put her in that situation, or flat out ignore it. Remember consoling is a form of you having to reassure her, she got attention. Plus- she feels unsafe without you as you reassure- convincing her even more there is something to be worried about if on her own..
I say this because these behaviors are increasing- meaning the more you reassure, the worse it is getting. Assuring any dog when afraid only makes their thought of fear in concrete-...