Separation anxiety help

Hello, I recently, 4 weeks ago, rehomed a 1 year old pug. Before I got her she was owned by a 70/80 year old housebound woman who was in poor health. Due to this my dog had never been left alone, ever, she was also never toilet trained 🙃 now she won't let me leave her at all. I have managed to crate train her and she is very happy in her crate (sleeps in there all night and goes in regularly on her own accord) so I have been trying her in that when trying to leave and it's helping a bit. So far, I'm building it up slowly, couple minutes away, come back etc. I have just started her on calming tablets to try and help too. I don't feel like we are making any progress at all though. Has anyone else ever been in this/ similar situation and actually managed to successfully get to the stage of comfortably leaving the dog and them staying calm? If so any tips and how long did it take? Tia