no bumper; they all have to go through this; it's part of realising that they are a separate being and it will pass. Just keep reassuring her by still talking to her if you pop out of the oom for a bit, and always coming back! She'll figure it out in good time.
Like I said on your other thread, DD went through this, but now that she can crawl, she just follows me and is much happier about me leaving her.
I'm sure it had nothing to do with leaving her with your SIL.
DD's latest one is to get really shy. she cried when the milkman came round to collect his money last week, and she sees him once a week and is usually really friendly.