I think it will be easier to find a home for a 1.5 years old, obedience trained, very well-behaved & spayed female GSD than Jake an "older" dog. Have you looked into GSD rescues in your area? I think this girl would be "snatched up" quite quickly.

There will be time for more *big doggies* in your life but right now you have Jake who is undoubtedly very attached to you and his current living situation.

I would suggest helping your friend re-home "Lady" but don't make that home yours!