I wonder you did not set a rule which not let her bring anyone go to your home before she started the contract. Renew contract or not, it depends on her working performance, how to treat to your kids, does your kids like her or not, etc.
I suggest you to tell her what you want rather than you hide it in your heart, right.
Finally, if you do not want to renew her contract, just give her one month notice is fine.
I did give her a set of rules including asking her not to bring anyone home. In fact I gave her the rules 2 times (one time even translated by the agent), and I did remind her not to bring anyone home every time we were out of town.
Last time, my building security officer told me that someone (Indonesian) went to my place and my maid let her in. He asked me if I expected someone to come.
I was shocked because I didn't expect someone to go to my place while my husband and I went to work. When I went home, I didn't ask and see if she would tell me someone had come.
But she did't tell until I asked if someone had come. She said yes, it's my father-in-law's maid (living nearby). Then I warned her not to let anyone into my place without our permission, even someone I know and she should report to us anyone had visited.