Stanger anxiety 4 month old

So my baby girl will be 4 months next week and she’s starting to have strangers anxiety.

We usually are home all week just the two of us (dad in the evenings). Today we went over to my sisters house who she hasn’t seen in 2-3 weeks and when my sister held her she completely lost it. Even if i held her and my sister talked to her she freaked out. I really dont want my baby to be scared of people and inly want me.

How can I help her and make it easier for her to be held and to be around others