。
She didn't feel at ease around my friends.
Literal
She [topic-は] my friends [together with-といっしょでは] didn't-settle.
といっしょでは ('when together with X') marks the social setting in which the discomfort occurred. The composite particle splits as と (comitative 'with') + いっしょ ('together') + で (locative/circumstantial) + は (contrastive topic) — together specifying 'in the situation of being together with [X], (as opposed to other situations).' 落ち着く ('to settle, calm down, feel at ease') in the negative past 落ち着かなかった captures sustained unease. 友人 is a slightly more formal, written-feeling alternative to 友達.