I empathise with how you must be feeling about this apparent lack of love/visits/attention from your own Mother, I know that it must really hurt you, particularly when you are so close to your In laws.

Of course I can not even begin to understand what your Mum is thinking or feeling, but If I may I would like to offer a little advice, which you can take on board or totally ignore.
My first question, would be 1) "have you spoken to your Mum about this?"
2)"have you actually rung her up and invited her to your home?"
3)"Does she know how close you are to your inlaws?"

Now the first question may seem like a simple thing, and so might the second, but I think that they are both important points to consider.

A)My Mother in law, would not visit unless she was invited, even though we (and particularly me) told her over and over again, that she was welcome at any time, she still would not come with out that 'invitation'.
B)Also consider that your Mother may not want to appear as if she is interfering, and again, this may sound too simple but I know of more than one grandma who has kept her distance so as not to interfere, only to go exactly the opposite way, and not visit at all!
C)Getting to the third question, there is a real possibilty that your Mum knows the rapport that you have with your in laws, and is 'Jealous'......

Now, as I said at the beginning, this is only my advice, and you can totally ignore it and no one would possibly know.
Give them a little thought though, before dismissing them ok? LOL

In Love and Light