I think when she rants about how awful working parents are, that's a great time to say, in kind of a crestfallen tone, "Oh. I went back to work when Junior was 6 weeks old." Maybe even go one step further and say, "Are you saying I'm a bad parent?" And just wait to see what her reaction is. Maybe she's speaking without thinking, maybe she forgot about your choice, maybe she does think you're a bad parent in that aspect. Maybe she'll apologize and never mention it again.
When she starts to repeat herself with stories or opinions, maybe say something like, "You know, you've mentioned that before" or "Yes, you mentioned that last time" or "Yes, you told me that over lunch an hour ago." Make your tone a little bored and disinterested. She may not get it the first time, but if you always respond like that, she may realize that 1) she is repeating herself a lot; and/or 2) you aren't interested in hearing more stories like that, so she should stop.
Also, I don't know what you've tried so far, but if you want to be a little more forceful about changing the subject to something of general interest, or about something you're concerned about, I don't think that's rude. If she finishes with story A, jump in with your own story, even if it doesn't "flow" well, before she can go on to story B.