How can I give my brothers girlfriend advice without offending her?

So, my brother has a girlfriend and they’re having a baby next month and I’m beyond excited to be an auntie because I’ve been the only sibling with children so this one will be my first… but me and his girlfriend aren’t very close at all. It’s not like we don’t like one another we just simply don’t have a lot of things in common so we didn’t really talk much beside family functions and get together but since she’s been pregnant I’ve been trying my best to be more involved and make a better relationship with her before the baby comes… I even helped throw her a babyshower. However, I feel like when I try and give her advice concerning safety for the baby such as car seat safety tips because they didn’t have their car seat installed right at all… it was super loose and wasn’t strapped and locked into place so I asked them if I could show them the right way to put it in and they agreed but she seemed very defensive about it but still let me show them but later I found out that she said I really made her feel bad about herself when I felt “the need” to fix what she already installed and told my brother that she felt like I was stepping on her toes and that I think I just “know it all” because I have two kids already. Well today on instagram she posted a picture of her bassinet that she set up for the baby and it has a small pillow and a blanket inside and I really want to tell her about the dangers of having blankets and a pillows where the baby sleeps but I’m afraid she’ll get offended by my advice for her but on the other hand I’m very big on car seat safety and safe sleep for babies! Should I keep my mouth shut or how should I approach this situation without offending her? She’s due to have her baby within the week and I don’t want her to be upset with me especially since she and I are still barely getting to know eachother and I don’t want to put a strain on our relationship before it’s even started but I care more about my nephews safety so I’m torn.