Beatrice already knew to save the failure concoctions for when they needed it, but she did respond with a nod to his advice anyways.
When he bit the monster and drained it of blood, Beatrice was shocked. But then again, the man in front of her had pale skin...like Hyde had. She didn't comment on it and continued with him. She connected the dots in her head as she did, and came to realize that he was a vampire, and he was somehow related to this Dracula person they were going to see. 
After they crossed the ledge, Beatrice politely thanked Alucard. He could've easily left her behind after all.

After traveling a bit further into the castle, she asked out of curiosity, "...Hey, Alucard. What do you think...about good and evil in peoples' hearts?"