I think you should only worry about lawyers if the game turns out to be an Angrybirds type of homerun hit.
Still, even if that happened, Lorna's design pretty much boils down to blonde bombshell+pink onepiece+Laser guns. The onepiece part isnt even consistant, she's naked half the time :p
Also, why not just contact Azpiri? azpiri at free.fr it's right on his webpage.
Lorna is just blonde bombshell, all you really have to do is give her something more than that to indentify her and she's already a differeant character than Lorna, a single identifying accesory is enough. You already know I think that something should be something wacky to fit the atmosphere of bouncing chomping heads and guns.
EDIT:
https://www.youtube.com/watch?v=-2ikThZaHds did you know about this? :p
http://www.comicartfans.com/GalleryPiece.asp?Piece=950492&Aux=43975&From=gallery&GSub=117380&GCat=68688&UCat=0 check it, the original cover art.
Looking at Azpiri's art on that site, Phantis is supposed to be a different character than Lorna...as far as I can tell she's got a bit more angular hair and that's it :p You got the ok from the original creator, who probably commisioned Azpiri to design Phantis right? so you shouldnt worry after all :p
Still, knowing that the source character WAS just a blonde fucking every alien robot and human in sight puts everything in perspective. I think that <3 at the end was not rosy after all :p