Siena's Blast can tear a whole in the Earth's EM field and ecosystem, and split the Earth like a melon. It has the same effect of a Phoenix level Blast. Storm redirected her blast with her WINDS intermingled with a electricity. Cyclops helped block the residual energy while STORM directed it upward.
Storm could plausibly do the same with a pressure dome--she could use the densely packed air molecules mixed with a EM field or an Electircal field, basically doing what Mags can do.
The thing about storm is her versatility. Given the stpulations, Magneto can only throw hunks of metal at her. She can block these AS WELL AS offensivesly attact him.
Without his Blood rip, he has NO offensive attack that cannot be directly blocked and countered by Storm's air attacks to which he is susceptible.
If Storm was really wrtten to her full credit withstanding the energies she's harnessed and channeled through her, any magnetic force enacted against her would/should be countered. MAGNETARS in the Galactic Core anyone?? Really, any Neutron star has a magnetic field way beyond that of Earth's. Magneto's energies should/would be NOTHING to someone who can manip that.
Galactic magnetic field 0.00001 Gauss
Solar Wind 0.00005 Gauss
Interstellar molecular cloud 0.001 Gauss
Earth's field at ground level 1 Gauss
Solar surface field 5 Gauss
Massive star typical field (pre supernova) 100 Gauss
Toy refrigerator magnet 100 Gauss
Sun spot field 1000 Gauss
Jupiter magnetic field 1000 Gauss
Magnetic Stars such as BD+54 2846 12,000 Gauss
White Dwarf star surfaces 1,000,000 Gauss
Neutron star surface field 1,000,000,000,000 Gauss
Magnetar field 1,000,000,000,000,000 Gauss
Since that is not stipulated, we only have him hurling metal at her which can be blocked, and she can counter with more powerful winds of which he has 00000000.0000000 defense since even the great Magneto needs air to live.๐