Dealing with SIL

I am facing some issues with my older SIL. She is not married and does not have any children. Yet she will try to tell me what to do. She also got onto my nerves when she tried to do things to my baby, including giving her toys which were reportedly sterilised when I tried to move them away (my baby tends to put things in her mouth) and purposely moved my baby away from my sight so that we were unable to see each other (not sure why she wants to scare my baby this way). Sometimes I feel like telling her to leave us alone and that she can have her own kids to do whatever she wants to them instead of imposing on me and my baby. What would you do if you are in my shoes?