No bowing, as that's a masculine courtesy greeting, unless one of them is something of a rule-breaker/eccentric and wants to be seen to be so.
I'm pretty sure it would usually be a curtsey by the lower ranked woman to the higher -- the depth and style of the curtsey depending on the respective ranks I'd have said ie a low curtsey is a sign of greater respect than a quick dip-down, therefore extended to someone of much higher rank (well, that's how I'm going with it!). The higher ranked woman would be the one to start the conversation.
Where they are equal in rank, they might both curtsey to the same degree and it would be the older woman who speaks first. But I think in reality they would know who was the superior. Even if they had never spoken together, they would surely know of each other, and therefore where they stood in the social hierarchy and/or favour with the Crown/despot. If they were total strangers, then they would still probably be able to assess who was superior, in the same way we automatically size people up depending on what they are wearing, how they speak etc, since every thing they wore would proclaim social standing, not just wealth. And if the artist is working for money, she's likely to be down the social scale if the other woman is middle class or above.
An inclination of the head might work if they are of truly equal rank, but to me is usually something done in acknowledgement by the higher ranked person to the lower.