For me I had her at level 99, but before trying again I used 2 x strength ups and that worked just fine, they were each worth +5, although the pearls of strength are worth +8 (but they are very rare) hope that helps.
Viewing post in Solo Challenge Ryoko bugged?
The Strength up are found in several places in the game when you explore dungeons, The pearls are much rarer, you can get a pearl of strength from Coral in her rppm by bringing her a cowgirl milk and you can get a pearl of magic from her as well (you get to choose which each time) I know the pearl is +8 while the strength up is +5. I also picked up another 2 pearls but that was later at some point and you don't get to choose strength or magic. Hope that helps.
Sorry, I just read my post again, It should of course read "room" which is the middle of the three rooms at the bottom of the screen. You can't repeat it but I think you can take another pearl of stregth instead of magic - I took one of each, anyway I only have 2 of each in the game so far and I've played all the updates except the slave rebellion, I am postponing keeping two saves for as long as possible, hope that clears it up