Hi OP! I don't think anyones been very helpful to you. Regardless of when you get your child's ears pierced- that's your decision and if it's something that you decide is right for your child now, then do it.
Usually, when ears are pierced but the likes of Claire's it's done via an earring 'gun' and they'll have specific earrings that are suitable to use, so your best of finding earrings when you're in there. Having said that, I wouldn't recommend you go to Claire's to piece your babies ears.
Professional piercers will use a needle to piece followed by inserting an earring of your choice (I think, I've never had this done but this is what I've heard) and I think the earrings you've found are a good choice because the pointed backs are completely covered. I've seen many babies with the same earring backs. Also, you'd have to check how big the actual front of the earrings are. I'd think the smaller they were the better, as they'd be less visible. According to many on here a professional piercer won't do a baby so then you've solved the problem- you can tel your Inlaws it's not possible till x age.
There's also another option in-between the two above options. It's called the Inverness ear piercing. And is similar to the 'gun' method in that it uses an earring to pierce the hole. However, it's controlled in that the piercer will 'push' the earring through in a controlled manner rather than it being shot through. This system also has its own selection of suitable earrings that are fully sealed etc.
I don't know what other options there are but these are the ones I know of. You can google and see what's close to you and what works for you.
Having said all of that, if you don't want to have your child's ears pierced. Don't. You're her parent and need to advocate for her, now when she doesn't have a choice in the matter and from now on when she needs your support.
Good luck!