I would assume that a Mistress who does not have foot or leg photos is relatively new to the scene. If she's definitely very experienced and has no such photos up then it might be appropriate to assume she does not enjoy those activities -- but that would be quite rare.

I second the advice to ask where you can see those photos. I'll also add that there's a good chance they're posted on social media even if they are not prominently displayed on her website/ads and it might be worth checking that out before making contact.

You may have to pay to view them. I know of at least one Mistress who intentionally paywalls her feet. Chances are a few foot and leg photos won't cost you much.