We know from tGS that Cadsuane does not sleep with her ornaments. Since she doesn't wear them 24/7, I believe that she has kept her defensive skills honed even if she has had little practical use for them. And since most Aes Sedai probably haven't had much practical use for them ever, I doubt she's less skilled at it than most Aes Sedai.

Since she knows of the Black Ajah (didn't she almost root it out, once?), it would seem likely that she'd acknowledge the possibility of being attacked sometime when she's not wearing the ornaments. So I doubt she has neglected her defensive skills.

I also do not see her as someone who'd reveal her best weapon (or defense) as soon as possible. If she can defend herself without relying on the ter'angreal, I believe that she would. That way, she'd get practical experience, and she'd only use the ter'angreal as a last resort, which means that only someone skilled enough to bypass her defenses or catch her off guard would know of her ter'angreal - and that would ruin the chance of killing her by suprise, or in that moment when she didn't have time to make a warding weave.

That seems a much better strategy in the long rung - the less the enemy knows about your super defenses, the better.