OK, so it doesn't appear to be an onerous raise.
As for the lease issue, a lease protects both of you. But if you fear not being able to afford the house, ask for an early termination clause or a clause that requires 60 day notice to vacate. That would protect her if you have to move earlier, byt giving her time to find a new tenant and protect you, by allowing you to move without obligating you for the balance of the lease.