My gf got malaria and typhoid long ago. will it come back?

Usually Not: Usually not unless exposed again. Once properly treated both infections are usually over. Rarely, some people go on to become carrires of typhoid (can pass disease on but are not sick themselves). There are 4 types of malaria each with a different lifecycle. Some types can relapse up to 5 years after intial infection. Her doctor can review the spefics of her infections with her.

No: Assuming your gf was effectively diagnosed and treated (and not re-exposed), she, and you, need not worry about either infection coming back.