Em is regularly playing 50ks I don't really think you can expect to be playing anyone outside the top 300 in these tournaments. I think she is overranked at the moment certainly not on form and perhaps a few 10ks after the grass might be a good idea. Otherwise she is unlikely to remain top 500. I can appreciate though the doubles form may persuade her to remain entering challengers.
It's a shame Katy doesn't have a better serve for someone of her stature it's surprisingly weak. If she had Naomi on a good days serve she would be a top 150 player.
But that's like saying 'if Naomi had Katy's movement and balance, she'd be top 100'.
And don't quite know what you mean about her 'stature' - Katy is only about 5 ft 6 or 7 or so (I'd have said). Naomi is over 6 ft. It's obvious a tall player should have a big serve advantage. Of course Katy's serve could get better (as could Naomi's use of her legs) but if it all was perfect, they'd all be top 20. I guess they all work on their game, weak and strong points, some areas with more success than others.
Meanwhile Tara, at least, seems to be doing well. 4-0 and serving.