Perhaps you mean Dynaheir. From the looks of things Denarius is a roman coin.
The answer to that would be it depends on what you are looking for in a mage. Dynaheir (with two tomes of wisdom) can dual class into a cleric. So these things aren't necessarily as cut and dry as they first might appear.
Edit: If you are talking about Dynaheir then yes you can get rid of her.
If you are talking about Dynaheir, if you ask her to leave, Minsc will go as well. I think Edwin is hilarious, but he is evil, and that doesn't always work with the rest of your party. Also, if I remember correctly he can't cast Identify which can get very expensive unless you have another party member who ca use that spell.
Best mage is your protagonist with proper stats and items. If you do not want a mage protagonist, though, you can always use imoen, and/or edwin, and/or zhar, and/or dynaheir. For arcane purposes.
Alright then. Well, Edwin is one of the strongest mages in the game, and Dynahier... Isn't. Shockingly, Minsc *will* play nice, but Edwin will leave if your reputation gets above 18.
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The answer to that would be it depends on what you are looking for in a mage. Dynaheir (with two tomes of wisdom) can dual class into a cleric. So these things aren't necessarily as cut and dry as they first might appear.
Edit: If you are talking about Dynaheir then yes you can get rid of her.