Weird greetings?

Am worried about the way Summer greets people.
When someone comes into the house, comes downstairs in the morning, or meets strangers in the street, she completely collapses on her tummy and looks like she is in trouble, even though she is wagging her tail, we all make a fuss of her and she still does it, she never jumps up, just lies on her tummy, she has never been shouted at when we have come in even though she has had accidents when we have been out, pointless telling her off when she has probably done it an hour earlier and forgotten, so I dont understand why she looks so scared when we greet her, she even does it outside on walks when she meets other people. I have never come across this before, every dog I have met in the past has either jumped up me or stood or sat and got excited. She even does it if i have been upstairs for 10 minutes and she hasnt done anything, I just dont understand. Even if you call her to you, she vertually crawls along the floor to get to you.
Any ideas?

Its being respectful for you , it may look not nice but it is better than her coming bounding over knocking you flying .
If you really dont like it try ignoring her no greeting (thats easier said than done)

She could give mine some tips. I get in from work and her bum and tail waggle so much she looks like she is about to take off, and then she kinda bares her teeth and growls! I find it very amusing, other people are not too sure though. I think they are all different Xx

She's being submissive to you - showing you respect.

If you ignore it for a while she might grow out of it.

she's being a good girl and submitting showing she is friendly and a good girl dont worry about it

Thanks all, feel better now, thought I was doing something wrong, I know I would rather this than her knocking me flying and if she knows at 13 weeks that I am the boss then thats fair enough, at least I know she wont knock a small child with her overzealous meetings, so thats a good thing.
I am definately going grey with the worry this dog is giving me lol, silly over reacting mommy that I am lol

She's just showing respect and is a good "problem" to have.

Spartan does this sometimes, it looks kind of cute.Lol.

Lottie does this i find it cute as its she kinda bounces her head around when shes laying down