Thestrals are not bat ponies! They're Undead reptilian like horses with bat wings! Don't believe me then go read some Harry Potter or watch the movies if that's to much to ask.
Some lifestyles are hard to change. For a human with no special talent, you had to stoop to a lowly position in society just to make ends meet. Tonight's customer is special. She's the only one who used to believe in you and thought you could stop.