Normally a vehicle is shared among two people who live together. In that case, the insurer would assign the highest-rated operator as the principal operator. You're allowed to invite another operator to use your vehicle who DOESN'T live in the same household on the RARE OCCASION, but this sounds like a more frequent situation. Be sure to disclose the arrangement to your broker/agent so that you have done your due diligence. Depending on your ages and the number of years that you have held your M2, the premium might not be all that different between your girlfriend and yourself anyway.
As other members have mentioned, things could get a little hairy in the event of a claim. Should you be involved in an at-fault collision, it will be reflected in the insurance history of the person who owns the bike. For this reason, I never lend out my vehicles unless it's absolutely necessary and someone I really trust and have a very close relationship with.
