Glad you're enjoying itm Will take a look at Bertha's behaviour.
Viewing post in Renegade Amiga Enhanced comments
Looking at videos of the arcade, it seems she charges at the player for longer, and more or less whenever she has the chance. You can fly kick her on the charge and knock her down, and that's the best way to beat her. That's what I did on the Spectrum version, too!
Currently that doesn't seem possible here, as she's just occasionally charging for a second or so and then breaking it off.