Even if you have fully repented, can you still feel guilt?
Yes, you can. Apparently it happens often enough that the Brethren have felt the need to address this issue on more than one occasion. Consider the following:
Elder Anthony D. Perkins:
Start with yourself, and forgive others as well. If God will not remember our repented-of sins, then why should we? Avoid wasting time and energy reliving the past.
To forgive yourself and others, you must trust the Atonement of Jesus Christ. The Great and Wonderful Love
Elder Richard G. Scott:
Now if you are one who cannot forgive yourself for serious past transgressions—even when a judge in Israel has assured that you have properly repented—if you feel compelled to continually condemn yourself and suffer by frequently recalling the details of past errors, I plead with all of my soul that you ponder this statement of the Savior:
“He who has repented of his sins, the same is forgiven, and I, the Lord, remember them no more.
“By this ye may know if a man repenteth of his sins— … he will confess them and forsake them.”
To continue to suffer when there has been proper repentance is not prompted by the Savior but the master of deceit, whose goal is to bind and enslave you. Satan will press you to continue to relive the details of past mistakes, knowing that such thoughts make forgiveness seem unattainable. In this way Satan attempts to tie strings to the mind and body so that he can manipulate you like a puppet. Peace of Conscience and Peace of Mind
Elder C. Scott Grow:
If you are suffering from feelings of guilt or remorse, bitterness or anger, or loss of faith, I invite you to seek relief. Repent and forsake your sins. Then, in prayer, ask God for forgiveness. Seek forgiveness from those you have wronged. Forgive those who have wronged you. Forgive yourself. The Miracle of the Atonement
So Amy, if you or a friend, are struggling with this, perhaps it is time to study more closely the Atonement. You can ask your Bishop for help, but most importantly, ask your Heavenly Father.