Should I trust my gf?

My girlfriend's ex girlfriend asked her if she could stay the night due to an argument with her mother. My girlfriend asked me if that was okay with me and I said yes. Now do you think I should stay the night like I always do or not? I trust my GF, I'm just iffy because at the beginning of our relationship she cheated on me with her and broke up with me because she was still in love. Its been 7 months and she now claims to be in love with me. What should I do?