Unless they want that to hit Mars hard, while the martian defenders are hurrying to defend Earth. It all depends on how many ships they need to provoke such an attack and how many others still remain to carry out the attack on Mars.
Oh and also wether the Martians take the bait and send enough ship towards Earth to seriously compromise their own defense and how quickly they can return to Mars, after they get wind of the GTVAs plan.
I really don't think the Lucy's beams were powered up in AoA. The next beam down from HRed is LRed and it seems odd that the superdestroyer which destroyed two, three, maybe more civilizations would have no greater firepower than a common Ravana or Demon.
I also seriously doubt that Sol, after 50 years with a population greater than the entire GTVA combined and the technology to perfectly manage them all, hasn't developed an answer to the Lucifer's shields--even if that answer is simply more warheads than the Lucifer's shields can take. An elegant solution, to be sure.
I did a little experiment in FRED once and found out that the HRed need about as many salvos and time to kill an Orion, as the superlaser needed in FS1, suggesting roughly the same damageoutput. On the other hand the GTVA did improve their armor technology in those 32 years, so maybe the Lucy had to strengthen their beams to compensate. Also the FS1 Lucifer didn't have side-mounted beams, or at least never used them while it's shields were on (ie every time is was ingame, except the last mission.... where no capship was present).
Either way the worst problem with the Lucifer was never her immense firepower, that is something that can be overcome. The real problem was her invulnerbility to anything the GTA and PVE could bring onto the field of battle. Even without the shield, she still packs a ridiculous amount of HP for a ship it's size.