I think the "forcing time" thing is kind of a cop-out.
I get it: you've been together for a while, you have a kid. There isn't as much excitement as there used to me. There is a routine. There might be less intimacy.
But it's a vicious circle. The less you date, etc, the less she'll feel like it. She's waiting to feel like she wants to do it with you, but she won't until it happens. I remember reading a study saying that while it's agreed people who are the closest years into their marriage still date regularly, they're close because they still date, not the other way around.
If she doesn't want to plan something, see if you can plan it with the GF and surprise her. Go to dinner and a movie, or even a show, or a class for something you both like. Try to spend time together in a non-matrimonial context. It's important for your relationship.
About the amount of sex, I believe it's not a competition, and sexual desire is unique. It just may be that with you, for your relationship, she feels twice a month is the right amount. Then forcing more would be a terrible idea, and preventing her from having more sex with other partners is probably a bad idea too. So I think I would focus on the quality of the sex instead. Try new things, or go back to doing things you did when your relationship was new. Could be sexual, like a sex act, could be romantic, like a massage or a bath together, you name it.
In the meantime, it seems contact helps a lot with intimacy. If she's not touch-repulsed, try and hug her often, caress her hair, arm, etc, kiss her... these little things can go a long way towards feeling appreciated.