If you already have Viconia's shield, did you try your luck with the Mirror of Loss for additional Wisdom? I like Alert on my low Dex group members and it usually does its job to push them to early spots in the initiative. The rest probably depends on how good your spell save/attack and your constitution are in general.
Yes, dice failure on all chars except Astarion who got + 2 Dex up to 22 Dex.
So, for me, I would choose upgrading her wisdom to 20 and picking Alert over Warcaster. That is what I always do and it works fine. I play her as trickery domain then life domain, however. There is an amulet in Jaheira’s basement that gives you +1 wisdom. However, it’s very special to Jaheira and personally I would only have her wear it. There is also a helmet or two that increases initiative in Act 3.
I will probably do this. Yesterday I stumbled into the fight with Gortash and his fists (although I only wanted to look for Ansur), Shadowheart (20 Wis, Alert) lost concentration one time, that might be ok.
I'm very reluctant to use potions or scrolls in this game, but I will look for it. I don't think that I can produce them however.