This file details some considerations to make for a Bastila build, and may eventually contain a few Bastila builds from different playthroughs. We'll see how far I take it.
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Bastila is a Jedi Sentinel.
She has great DEX (18), but otherwise fairly unremarkable stats, with her only other stat higher than 12 being CHA (15). As benefits her Sentinel class, she's not particularly bad at anything, with no stats less than 10.
Bastila is required to be in your party ... well, a little, but less than you'd think, considering how central she is to the plot. In fact, she's actually unavailable a lot. There's one mid-game planet you're never allowed to use her on (without cheats). Depending on the order you choose to complete planets, that may increase to two planets. That's without even talking about the end game where, for Light Side playthroughs, you permanently lose here as a party member with quite a bit of game left (and even for Dark Side playthroughs she's only available for about half the end game). Adding this all up, in the most extreme case, she's unavailable for about half the game. At the other extreme, she can be available for around three quarters of it. (I really should measure that sometime and come up with actual numbers...)
The point of all that is, while Bastila can be a very valuable party member, you should also plan for times when she is not there.
Bastila suffers the cost that all Sentinels pay for their versatility: they don't excel at anything. Her extremely high DEX probably tilts toward an elusive melee build. But her CHA isn't bad, and gives the same benefits as WIS to casters (WIS also does a few other things that make it generally preferred for companions, but those are relatively minor). So making her a caster is also viable. Bastila joins the party at a fairly low level (3), allowing more opportunity to affect her early build than some other companions.
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Bastila Builds:
Melee Bastila
Caster Bastila