What’s the etiquette with ppl who talk to themselves?

[CoolGirlsNeverGetAngry]

I’m a couple of days in to a four week stay with my MIL (I’m currently on Mat Leave). It has become apparent to me that due to the fact she spends rather a lot of time on her own she tends to talk to herself and I generally only catch the last few words “mumble, mumble get the pans”.
I’ve kind of got to the point where I’ve stopped asking her to repeat herself because I quickly realised she is not actually talking to me but it also means i’m frequently ignoring her when she is speaking to me because it’s not always clear. She also frequently talks to the baby very quietly and i’m not sure if I supposed to respond by answering her question or just stay quiet. The baby can’t talk so I’m guessing she’s not expecting an answer.
Any ideas how to deal with this? I’m tired of constantly saying “sorry?” but ignoring her seems quite rude. It’s extremely draining.
I know this is stupid but i’m going to be sharing her space for the next month.

I talk to myself a lot too. I didn't realise how much until I changed jobs and started working in an office with only one person rather than 10+ and could hear myself! My colleague quickly got used to when I was talking to myself and when I was talking to her and actually I think I've reduced a lot how often I do this.

I don't think there is much you can do except perhaps let her know that if she wants your attention she needs to say your name so you know she is talking to you?