There aren't any other ways to fight her. I'm not sure if the devs will add alternate options to access her (she's technically more of a bonus boss) but you can hope, I guess?
Also, have you tried getting a key to the C-4 from Sophie? It may not be all over for you yet.
you don't need the maid tf to get the C-4. All you really need to do is when the vampire Magical girl is in front of isabelle's door speak to her. when you get a list of options go to "all the doors are locked." she will mention she has a key and will give it to you in exchange for some blood. do it an you get the key with no need for the maid TF.
Thanks for this information! I never went to the house at evenings so I never saw Sophie there. I will try it out!
Also...Is Vampire TF planned?