DD has had this same problem too, tooth removed at only 2yrs as a result :(
I felt like cr@p about it too, you can't help it, but I also knew she'd had an exceptionally healthy diets, & not even any sweets etc at that age,
the Dental Hospital Doctor did say that it can be down to milk in a bottle concentrating it onto her teeth, our Dentist agreed with this, but also said about the weak enamel making her more vunerable & it was something that just wasn't properly understood, I was doing all the right things with her diet, teeth cleaning etc & to not blame myself :)
I do have a good friend who works in Alt health care, & she reckons there are some studies on this from that angle, & a theory is, that Mums under a lot of stress during pregnancy seem to see this problem more often in their kids, it certainly fits with me, & with a few other families I know, whose Kids also suffer with this.....
if this theory is true, then realistically, you can't blame yourself, stress happens & can't always be avoided, even if you DO know its not good for baby
There is a coating you can have put on their adult teeth if she is still worried then, a friends had both her Kids teeth done, & it seems to have helped, as now adults & no problems I've spoken to our Dentist about this, & he has said it might be a good idea, but to wait & see how her teeth are when they've all come through