5pb. is a very good mage like character. She has good INT and SP to back up her mage qualities. She has decent VIT, MEN and HP allowing her to take some hits. She has an AoE healing skill and SP Skills. Her downside is that she has to come up close to damage enemies via Combo Skills. Additionally only her Break skills do magic damage. She can of course just use SP Skills but she will eventually run out of SP unless chips were made to lower the cost of the skill and restore her SP. Her passive, Null Seal Skill really helps her attacking with only SP Skills. Her EXE Drive Skill is magical so she can do quite a bit of damage with it.
With her Break Skill "Slow Down", she can delay the turn of the enemy, which is very effective in boss battles if you put her together with Neptune and Uni, who both have EXE Drive Skills that can also delay the enemy's turn. With a fourth party member that possesses the EX Finish "Combo Link" and has a 8-hit Rush Skill (Vert or Blanc), the fourth member can easily fill the EXE Drive Gauge, while 5pb., Neptune and Uni prevent the enemy to get their turn.
If you put her as a support party member however, since her assist attacks are all magical, you can ignore her bad movement and lack of magic Combo Skills. You also don't need to worry about her lack of SP.