The per donee exclusion is now $12,000 and will go to $13,000 on 1/1/09, and if her step mother is still married to her father, the exclusion is double ($24,000 or $26,000) since the gift can come from both parents. I believe the balance will count toward the step mother's $1,000,000 lifetime gift tax exemption, although she may still have to file some form with the IRS.
If the stepmother has already exceeded her lifetime exemption the balance of the $200,000 (the portion above the per donee exclusion amount) would be taxable at 32%.
Caveat: if I recall correctly, the "lifetime" exemption is also a "deathtime" exemption, so if your girlfriend's stepmother eats into her lifetime gift tax exemption before she dies, the ability of her estate to make tax-free bequests will be correspondingly reduced.
Free advice is worth what you pay for it, so check all of the foregoing with a good accountant.