I think the main thing with BLW is that they are sitting up well, but remember there's certain foods that should be left until after 6 months I can't remember which as we've waited but I think it's grains, dairy? Tbh BLW is very slow in the beginning, if you do it true to form it could be weeks before they even manage to eat much, it's a lot of sucking and gumming in the beginning. She's not likely to be getting much to fill her up so you could look at that from two angles 1) you may as well wait as it's not likely to fill her anyway so may as well give more milk, or 2) if she's not gonna get much it doesn't matter if you start a bit early and if she does then maybe she was ready. But I'm a bit nervous about the whole digestive system situation which is why I waited until 6 months no matter what other signs but that's because I BF I know it's different if FF. Sorry load of waffle, but yeah maybe you could try a bit of fruit or veg sticks? Something she could suck and gum to practice to coordination?