In the meantime, here is one prayer of St Gemma and one prayer to her that I found.
Prayer of St Gemma
O my crucified God, behold me at Your feet; do not cast me out, now that I appear before You as a sinner. I have offended You exceedingly in the past, my Jesus, but it shall be so no longer.
Before You, O Lord, I place all my sins; I have now considered Your own sufferings and see how great is the worth of that Precious Blood that flows from Your veins.
O my God, at this hour close Your eyes to my want of merit, and since You have been pleased to die for my sins, grant me forgiveness for them all, that I may no longer feel the burden of my sins, for this burden, Dear Jesus, oppresses me beyond measure.
Assist me, my Jesus, for I desire to become good whatsoever it may cost; take away, destroy, utterly root out all that You find in me contrary to Your holy will. At the same time, I pray You, Lord Jesus, to enlighten me that I may be able to walk in Your holy light. Amen.
Prayer to St GemmaIncidentally, many websites list 11 April as the "Feast Day" of St Gemma. That is indeed the day of her death (she in fact died on Holy Saturday). However, Fr Spencer and the Passionists seem to celebrate the feast day on 16 May (see the post Saint Gemma for last year's feast day.)
O Most Glorious St. Gemma, Mirror of innocence and penance, may we who humbly invoke thy Heavenly intercession obtain from thee the grace of purity in all our thoughts, words and actions. Amen.