Autistic mother in law

I'm looking for some advice on how to cope better with my mother in law who I have suspected as having some sort of Autism since I met her more than a decade ago (she's now in her 70s). As far as I am aware, she has never sought a diagnosis - but sometimes I feel like she might be aware that she is different to other people. As for my husbands family - there is a mix in terms of who does and does not think she does. My husband is reluctant to talk about it, I think he thinks I'm being nasty for suggesting it, even when I say that a diagnosis might help us understand her better. For my husbands immediate family; I guess it's what they're all used to so they just block it out and then occasionally get very angry with her when her behaviour tips into the unmanageable. My FIL has a strange ability to act almost as if she isn't there at all.

The reason I'm looking for some advice on here now is that we now spend a lot more time with my MIL now my husband and I have children of our own. And to be honest, I now dread the times we see her. I find myself becoming incredibly anxious because I feel trapped - I'm acutely aware it's not my place to 'manage' the conversation (on any topic, nevermind bringing up one on Autism) but it feels like everyone is in a constant state of stress the whole time she is there. 

I understand that she herself is probably finding the situation difficult - and that's why we see such an intensive display of some of the most challenging communication behaviour i.e. repeatedly telling the same very long detailed stories with no narrative (but packed full of pointless detail) using the exact same phasing/ words/ sentences and even the same strange intonations on some of the specific words. She's incredibly bright and has a fantastic memory for facts and details. In this example - she will often continue even if you remind her she's already told you the story and she will often launch into it even if people are already having a conversation about something completely unrelated. If you try and continue the conversation you were having she will just tend to continue and speak even more loudly (often she will basically start shouting). If she's not telling one of these stories - she'll often parrot (pick out a word you've just said and repeat it) but she'll do this continuously the whole time someone is speaking and it's incredibly distracting. 

I don't know if this sounds like I'm being unreasonable (dangerous question to ask on a forum) - but it's just non-stop. I honestly don't think we've ever had a conventional conversation in the time I've known her as she is just constantly stuck on transmit. I know she doesn't read social cues, but even if you try and tell her/ redirect her - its like she cant hear you. I'm of course happy to listen to any stories she has (and often do, including the repeated ones) but how can we manage to spend time together as a family without her dominating the airwaves all of the time? She is also desperately keen to looking after my todder on her own, but some of her behaviours can be so erratic I'm not convinced my child would be safe. How do I say no in a way she will understand/ listen?