When I think about stuff like this, I feel the same way- it's difficult for me to tell people I care about that they are being hurtful... particularly if what they are doing is kind of in a grey area? Like, if they don't clearly know they are upsetting me.

I mean, you could start to approach when she says she's tired by relating to it clearly with your experience, you could express how you don't mind talking to her about how she is tired as long as it is a "sharing is caring" thing- like sharing strategies to resolve the situation, use the best of your energy, etc... and not just a completely whine session every time.

No one likes being dumped on constantly.

She DID choose to have a baby. But no one knows what that is going to be like until they actually go through with it.

If you don't want to support her, that is certainly your choice, and I really make no judgement about it. I have things that I can't be actively supportive about and I dodge discussion of such items like the damn plague.

But, this is one of the most important life events that she can go through... I don't know how recently she had the baby, but eventually she will adapt. She'll suck it up, realize she's in it for the long haul and being a parent is sometimes just about being tired- she can learn that from making friends with other parents much easier, though.

I don't know what country she is in, but if there are any parenting groups, mother social groups, play groups, etc... I would strongly encourage her to head in that direction.

Even something online- like a loose newsletter or something might ease any anxiety she may be feeling.

I mean ultimately you can pick what you support your friends in, but they can do the same.

If you make her aware that you don't feel comfortable having so many discussions specifically about the baby [for whatever reason, you don't have to say precisely], but in a caring "I want you to know because otherwise I'm walking around upset with you and I don't want to be upset with you for something you aren't aware of" kinda way?

You and her should be able to work around all of this, in some way.

If you can't... it's more likely that issues just abound.
...but I mean, something to think about- pretty much everyone goes nuts when they have a kid. It's like a biological imperitive. Then eventually they realize the rest of the world exists again.

I've gone through it with several friends- they are all good people, but they did go a little out there.
They came back.

Have you thought about video calls/skyping?

ETA:
ALSO- you are not being horrible at all.
I think it's difficult to remember that other people don't see how we struggle through the world when we have things like constant fatigue or anxiety or ptsd... especially if we "present well". [I have the impression that your friend thinks this]

So sometimes we have to actually tell them. It's not really fun, but the alternative is fostering a growing rift.