Go for it!
Fighting Style - a girl can't go wrong by picking Defence :P
I'd go with Life - she is a Healer

Stopping at lvl 4 IS tempting, I know, but lvl5 gives some fun spells.
At CHAR lvl 7 I'd go back to Fighter, for Action Surge.
Hah. Thought I maybe could have been clearer when I wrote my OP...
Yeah, I was thinking of going to
Cleric level 5, so character level 6, before switching back to Fighter.
However, instead of BM or EK - how about ... Ranger instead of Fighter? You lose less on ESL yet gain the same Weapon and Armour (if you take RK) Proficiencies. And still get to use that WIS stat. You also gain potentialy up to three - although IMO two is "more like it" - Skill Proficiencies - one from Ranger, one from Favoured Enemy, and Sleigh of Hand from Urban Tracker.
Huh. Hadn't even considered moving her away from Fighter entirely... That's whole other kettle of fish... Something to think about for sure.