Yes its allowed.
But my recommendation is always avoid it and find a shia girl.
Because in the end a shia mom will teach her about ahlulbayt a.s and teachings of masoom a.s which a sunni mother can't teach.
There will always be a conflict in naming a child, praying way, breaking the fast at iftaar (timings), prostation on clay, and many more.
Believe me things will conflict.
i have personal experience.
If you trouble finding a shia partner, i can recommend you put a profile on shiamatch.com