Well, she's infantilising you and treating you like a child. But if you live with her rent-free, have a baby despite not being able to afford anywhere to live - what do you expect really? She's probably frustrated with you.
A few nice outfits help you to prepare but if you don't have much money, it's basically only stuff the baby will puke and poop on. Ditto prams, cots etc - secondhand is sensible if you don't have much money.
How does she actually feel about having you living with her, and having the baby around? Is she genuinely looking forward to it, or doing it with gritted teeth to help you out? I think you need to sit and have a grown up conversation about it, and also develop a plan for how and when you will move out.
Having a baby hits you like a ton of bricks, she knows that and you don't. You need to find some dynamic that means you benefit from her experience without it feeling overpowering and infantilising.
You could actually draw up ground rules eg, here's our savings plan, so long as we save up regularly then the rest is ours to spend as we wish, she can't come into your room without asking permission etc - but equally she might have rules about where you leave mess or baby things, how much you can ask of her, how much you contribute to housework and cooking etc.