Dynaheir

Dynaheir is a Lawful Good Invoker (Specialist Mage) who can be recruited in BG1.

Baldur's Gate 1

Dynaheir can be found in the Gnoll Stronghold, the location of which will appear on your map if you speak to Minsc or Edwin in Nashkel. She can be recruited from chapter 1 onwards and has no side quests. You do not need Minsc in your party in order to recruit Dynaheir, but if Minsc is ever in your party at the same time as Dynaheir and you remove either character, the other will leave automatically.

Unless you are playing a mage, Dynaheir is probably the best option for a good party (Neera is more powerful, but comes with the side effects of wild magic).

Siege of Dragonspear

Dynaheir can be recruited after the first chapter of the game. This time she can only be recruited at the same time as Minsc, so you must have (and keep) both characters in your party.

Baldur's Gate 2

Dynaheir does not appear in Baldur's Gate 2, for reasons which are explained at the start of the game.