Hold the fort. The bottom line it is YOUR decision. And this 'parenthood by proxy' mentality gets more married couples in trouble. The decision has to be for yourself, what is in your best interest because ultimately (if there was to be a kid) that would determine if a kid would have a good home to grow up in.
Also, the decision not to have children is, in a way, a repudiation of her existence so there is a bit of 'misery luvs company' attitude, or "I enjoyed it so much, I want her/him to enjoy what I had."
Trouble is, you get ma to admit it, have to really back her into a corner..
Depending on how bad she has the 'baby rabies', it may determine how much contact you have with her. If you cannot have a decent conversation without it degenerating into a 'why don't you get pregnant' scenario within minutes, it is time to limit her contact.. before she strong arms you into a decision you will regret.
two cents ¢¢