You could possible help to calm things down by reassuring Bella that her pack position is safe - since she will be the one feeling pushed out.
Try and spend some time with Bella on her own, out of sight and hearing of Lola. Make a big fuss of her, and talk to her, play with her favourite toys, take her out for a walk on her own, and so on.
You can do the same with Lola, so she feels welcome and accepted, and with luck, if both of them feel more secure, they won't be pushing for a superior position, which is what the fighting is all about.
It's worth a try, and if it doesn't work, you are where you are now, and may have to look at re-homing one or both of them.