Will have a post done in a short while.

Mitsuki can offer some distraction by using her mist cantrip.
She obviously won't use offensive spells (especially because Gavin asked so), but she won't be standing around for too much.

Since she is blindfolded, she will be able to use her "sixth sense" to feel the bullets coming, she will at least be able to defend the first ones aimed at her, but since they are using special equipments which affects magic, she won't be able to see them.

Tl;dr Mitsuki will conjure up some mist to cover her retreat, maybe conjure up a reflection to save someone or to further help her to get away.