MIL and cot 😧😧

So my partner recently told me that his mum wants to buy us a cot for baby since it's the first grandchild. Now this doesn't seem like a problem but she has no income, she relys on 2 of her other sons to pay her bills (which isn't alot since neither work regularly) and i don't want her to pay for something that's that expensive when she's struggling for money as it is. And of course my partner told her she could buy it without giving a second thought to her current situation (the cot we want is $400 which is standard price for a new cot where we live) . I just feel incredibly guilty when she's struggling so much already and i don't want to add anymore stress on her financially. I tried talking to him about it but he insists she'll figure it out and that he doesn't want to tell her no because she'll get upset. He thinks that i always reject the things she gives us (i don't and she's only given us broken things in the past before for example a lawn mower that wouldn't start and when it did it set itself on fire and a massive tv unit that's so big it didn't even fit in the house). I don't know what to do, i feel like it would be rude for me to say something as people tend to be quite private about money related things and i feel it would be out of my place to mention it since i don't know her very well so therefore shouldn't really know what her current financial situation is. I just genuinely don't want her to put herself in such a difficult position with such an expensive item but he won't tell her that and says that she shouldn't only have to buy the "small things". Like??? we haven't even asked her to buy anything. We haven't asked anyone to buy anything and i certainly wouldn't ask someone in her position to buy such an expensive item let alone anyone at all. What do i do?